Surface Acoustic Wave delay lines have been used as probes for chemical analysis. The interaction between matter adjacent to the SAW device surface and the propagating Raleigh wave caused measurable changes in the amplitude, phase and resonant frequency of the wave. The effectiveness of various electronic detection schemes was evaluated along with the response of the device to changes in pressure and temperature. A lithium niobate SAW device was used as a detector for gas chromatography. Frequency shifts of a SAW oscillator provided the highest sensitivity to compounds eluting from the G.C. column. Sensitivity and specificity of the detector to polar and non-polar organic compounds was greatly enhanced by thin chemical coatings applied to the detector surface. Submicrogram quantities of material were easily detected. Linearity and dynamic range of the detection system was poor. Numerous refinements remain to be made which could significantly improve performance. Thermomechanical analysis of thin polymer films were accomplished using a 32 MHz quartz delay line. Very large wave amplitude shifts were observed as the polymer reached its glass transition temperature. Tg measurements were performed on samples clamped to the surface and cast on the surface. Agreement with low frequency dynamic mechanical measurements was good for the clamped specimens, indicating the absence of wave coupling. Specimens cast on the surface experienced large Tg shifts and therefore were coupled to the surface wave. More subtle transitions were also detected. A crystalline transition around room temperature in a TEFLON film clamped to the SAW device provided an easily observed shift in SAW amplitude. Explanations of this behavior have been proposed. The SAW device also provided an ideal vehicle for examining the behavior of thin photoresist films on the surface. Information on solvent evaporation processes and photo-induced crosslinking rate was obtained. The attractive features of the device for polymer thermomechanical analysis include low cost, ruggedness, high sensitivity and ease of use. / Ph. D.

Matched filter detectors are used to detect known signal waveforms transmitted under noisy conditions. Moving-average matched filters (MAMF's) are a class of digital filters whose performance is measured in terms of Signal to Noise Ratio (SNR). The overall performance of a MAMF is described by the SNR Improvement (SNRI) which is the ratio of Output SNR (OSNR) to Input SNR (ISNR). The OSNR and ISNR are the SNR at the output and input of the MAMF respectively. SNRI is maximized by maximizing OSNR since ISNR is fixed for a received signal and noise. The OSNR of a MAMF is a function of the noise autocorrelation sequence and the transmitted signal vector. The maximum OSNR of a MAMF is produced when the signal vector is the eigenvector associated with the smallest eigenvalue of the Toeplitz matrix formed from the noise autocorrelation sequence. If the noise autocorrelation is not known in advance of transmission, or not stationary, then it must be estimated at the receiver. Since autocorrelation estimators derive their estimates from noise samples, i.e. a random process, the estimates are probabilistic. In a practical implementation wherein the signal vector is fixed, the noise is stationary over short periods of time, and the noise autocorrelation sequence is estimated, the SNRI or performance of the MAMF varies and can even become less than unity if either the estimates are poor or the noise characteristics differ from those expected when the signal vectors were selected. A SNRI less than unity is highly undesirable as processing, which is done with the objective of obtaining higher OSNR than ISNR, i.e. a SNRI greater than unity, has become counterproductive. This thesis proposes a variation to the classical MAMF communication system and investigates the performance of the resulting MAMF. In the classical MAMF communication system the N-dimensional signal vector is treated as a single vector. In the proposed MAMF communication system, the N-dimensional signal vector is composed of two or more linearly independent basis vectors spanning a signal vector subspace of dimension M. By combining the linearly independent basis vectors in the receiver, one can effectively change the transmitted signal vector to any signal vector in the signal vector subspace to maximize OSNR. The OSNR of a MAMF is a function of the autocorrelation of the noise as well as the signal vector. The autocorrelation of the noise is estimated in both the classical and proposed systems. For relatively few noise samples, the estimated autocorrelation of the noise deviates from the actual autocorrelation. The proposed system is formed from the classical system by proceeding the MAMF with a processor that extracts the received linearly independent basis vectors with additive colored Gaussian noise from the received transmission and combines them to yield maximum OSNR assuming the estimated autocorrelation of the noise is exact. Since the autocorrelation of the noise is estimated from the random noise process, the autocorrelations themselves are probabilistic and hence the maximum OSNR is too. As the estimated noise autocorrelation approaches the actual noise autocorrelation, the OSNR approaches the absolute maximum OSNR for the M-dimensional system. The theoretical aspects of both the classical and proposed MAMF communication systems are developed in this thesis. The performance of the proposed MAMF communication system is investigated for a practical implementation wherein the signal vector is composed of two linearly independent basis vectors and the noise characteristics vary over time. The performance of the proposed system is first compared to that of the classical system with both systems using various signal vectors, over various noise colors, and with the exact noise autocorrelation given. The performance comparison between the classical and proposed systems is then repeated with the noise autocorrelation, as in a practical implementation, estimated using either the classical biased or Burg estimator. The performance is measured by SNRI and the results are tabulated and graphed. Finally, the proposed system is implemented and its performance measured by bit error rates as a function of ISNR. This will show whether SNRI performance is a good prediction of bit error rate performance. The color of the stationary Gaussian noise is kept constant during transmission of a particular bit. The color of the stationary Gaussian noise is changed between bit transmissions to observe the robustness of the system under different colored noise conditions while maintaining the same signal vectors, or signal subspace. The results are again tabulated and graphed. / Master of Science

No description available.

No description available.

No description available.

No description available.

No description available.

The goal of wind-waves research is to predict the waves field and its effect on the environment. That environment could be natural or imposed by human endeavour. The mechanism of wind generated waves is described in the present work as a wind-bulk flow interaction rather than as a mechanical process which only transfers the wind energy to the wave. In the light of this description, the generation and growth of surface waves are functions of the physical properties of the interface, density of the bulk flow perturbations and wind shear stress. While the present models for the prediction of surface growth and evolution show some consistence - in some cases - with observations that were conducted in laboratories and in real fields, the work presented in this thesis justifies and explains the inconsistency or contradictions in other cases between the observations and the predictions. Also, physical interpretations for observations, for example wave growth with fetch, are suggested in the present work. To illustrate the physical mechanism responsible for wave generation and growth under the effect of wind action, two approaches are used. The first involves studying the effect of the physical properties of the water surface on atmospheric input into the bulk and thus the effect on the formation and growth of capillary waves. The second involves studying the correlation between the wave formation and growth and the density of the bulk perturbations. Wide ranges of previous data are used to analyse the effect of the physical properties of the water surface on wave generation and growth mechanism for the first approach. Also, a group of experiments using the PIV system (Particle Image Velocimetry) were conducted to study the correlation between the wind speed, bulk flow evolution and wind-waves‟ generation and growth for the second approach. The main physical parameters which are responsible for the generation and growth of capillary waves are determined. The Ohnesorge number is modified to predict the generation and growth of surface waves. In the second part, additional physical parameters of the bulk flow are introduced to illustrate the correlation between the wind generated waves and bulk flow evolution. A new parameter is used to scale the transition of the bulk flow from laminar flow to turbulent flow or the transition of the water surface from an undisturbed surface to a fully disturbed surface. The history of wind-wave research is relatively short. Although there were basic developments in the 18th century, a concentrated effort really began as a result of the military imperative of the Second World War. These developments were however, largely empirical. A theoretical frame work began to develop with the studies of wind-wave generation in the last century. The present work is conducted to fill some gaps in wind generated surface waves research and to introduce new approaches to simplify understanding wind-waves field and its effect on the environment.

Ambient seismic noise from generation to its application for determination of sub-surface velocity structures is analyzed using continuous data recordings from the Swedish National Seismic Network (SNSN). The fundamental aim of the thesis is to investigate the applicability of precise velocity measurements from ambient noise data. In the ambient noise method, a form of interferometry, the seismic signal is constructed from long-term cross correlation of a random noise field. Anisotropy of the source distribution causes apparent time shifts (velocity bias) in the interferometric signals. The velocity bias can be important for the study area (Sweden) which has relatively small velocity variations. This work explores the entire data path, from investigating the noise-source distribution to a tomographic study of southern Sweden. A new method to invert for the azimuthal source distribution from cross-correlation envelopes is introduced. The method provides quantitative estimates of the azimuthal source distribution which can be used for detailed studies of source generation processes. An advantage of the method is that it uses few stations to constrain azimuthal source distributions. The results show that the source distribution is inhomogeneous, with sources concentrated along the western coast of Norway. This leads to an anisotropic noise field, especially for the secondary microseisms. The primary microseismic energy comes mainly from the northeast. The deduced azimuthal source distributions are used to study the level of expected bias invelocity estimates within the SNSN. The results indicate that the phase-velocity bias is less than 1% for most station pairs but can be larger for small values of the ratio of inter-station distance over wavelength. In addition, the nature of velocity bias due to a heterogeneous source field is investigated in terms of high and finite-frequency regimes. Graphical software for phase-velocity dispersion measurements based on new algorithms is presented and validated with synthetic data and by comparisons to other methods. The software is used for phase-velocity measurements, and deduced azimuthal source distributions are used for velocity-bias correction. Derived phase-velocity dispersion curves are used to construct two-dimensional velocity maps of southern Sweden at different periods based on travel-time tomography. The effect of the bias correction is investigated, and velocity maps are interpreted in comparison to previous geological and geophysical information.

Approved for public release; distribution in unlimited. / Optical turbulence plays an important role in the propagation of electromagnetic waves through the atmosphere because it broadens and distorts the optical beam. A variety of optical, thermal, and acoustic instruments are used to detect the atmospheric turbulence and an acoustic echosounder has proven to be a valuable tool to probe the fine dynamic structure of atmospheric turbulence within first hundred meters above the surface. The first planar acoustic echosounder constructed at the Naval Postgraduate School was by Weingartner and Wroblewski, under Walters' supervision. Moxcey later modified this design by reducing the number of drivers from 25 to 19 and placing the drivers closer together into a hexagonal, close-packed array. This thesis explored the potential sources of the transducer ringing and implemented solutions to the problem. Additionally, we also improved the receiving sensitivity of the echosounder and lowered the electronics noise when receiving. Finally, we applied these techniques to another array assembled with new drivers to improve its performance compared to the previous echosounder array, while measuring and quantifying the level of improvement achieved. / Lieutenant Commander, Republic of China Navy