Thesis (M.Sc.)--City University of Hong Kong, 2005. / At head of title: City University of Hong Kong, Department of Physics and Materials Science, Master of Science in materials engineering & nanotechnology dissertation. Title from title screen (viewed on Sept. 4, 2006) Includes bibliographical references.

Thesis (Ph. D.)--Drexel University, 2007. / Includes abstract and vita. Includes bibliographical references (leaf 195).

One of two Project Reports / <p> This report describes the basic physical properties of surface wave devices and design procedures necessary to realize filter functions from such devices. The mathematical form of the surface wave is presented. Filter models based on this wave are reviewed and the strong relationship between device geometry and resultant transfer functions is developed. </p> <p> Design and experimental procedures adopted for the synthesis of a surface-wave filter used for colour T.V. I.F. strips are given. Two such filters are actually made in the laboratory and experimental-theoretical results are compared. Results obtained indicate good agreement between theory and experiment, and clearly demonstrate the superiority of surface wave filters over conventional L-C filters in high frequency applications. </p> / Thesis / Master of Engineering (ME)

No description available.

A general, non-iterative design technique for low shapefactor, transversal filters is presented. This design approach uses two cosine series to specify appropriate eigenfunctions. An infinite set of such eigenfunctions are defined and the method for choosing the coefficients is discussed. The total filter response is specified as the product of two individual frequency responses. The impulse response of each is then determined by applying the superposition of appropriate eigenfunctions. The criteria for choosing the appropriate eigenfunctions is discussed. A synthesis procedure for designing surface acoustic wave filters is presented. The effects of truncating the impulse response are also explored. A design example is shown for a filter with 10 percent fractional bandwidth and a shapefactor of 1.15.

This thesis introduces a solution to the problem of time and memory space requirements associated with the manipulation/creation of solid state device layout. Through the use of a hierarchical organization of data and a tailored indexing technique, the software described here, referred to as Saw Draw, is capable of manipulating huge amounts of data in a short period of time. This program was written for surface acoustic wave (SAW) device layout but works for a broad range of devices to include semiconductors, microstrip and others. Due to the large number of details which must be stored for each SAW structure, simply displaying a typical SAW device can become exceedingly tedious. When an entire mask of devices is organized, disk storage requirements can become prohibitive. This software has been designed to minimize both of these critical problems. This work describes the capabilities, structure and special algorithms used in Saw Draw. Included is an example of how a SAW device might be created and a listing of the program code in the Appendix.

Acoustic metamaterials have been shown to support acoustic surface waves when excited by a broadband signal in a quiescent environment and these waves could be manipulated by varying the geometry of the structure making up the metamaterial. The study presented here demonstrates the generation of trapped acoustic surface waves when excited by a turbulent flow source. The metamaterial and flow were interfaced using a Kevlar covered single cavity whose Kevlar side faced the flow to ensure no significant disturbance to the flow and the other side was open to a quiescent (stationary) environment housing the metamaterial. Acoustic measurements were performed very close to the surface of the metamaterial in the Anechoic Wall Jet Facility at Virginia Tech using two probe-tip microphones and correlation analysis yielded the structure of the surface waves. Two different metamaterials; slotted array and meander array were tested and characterized by their dispersion relations, temporal correlations, and spatial-temporal structure. The measurements proved the existence of surface waves with propagating speeds of a tenth of the speed of sound, when excited by a turbulent boundary layer flow. These waves were much weaker than the overlying flow exciting them but showcased excellent attenuation properties away from the source of excitation. Measurements along the length of the unit-cell geometry of the metamaterial demonstrated high coherence over a range of frequencies limited by the dimension of the cell. This was a surprising behavior provided the cavity was excited by a fully developed turbulent flow over a flat plate and indicated to an area averaging phenomenon. A wall normal two-dimensional particle image velocimetry (2D-PIV) measurement was performed over the Kevlar covered cavity and a smooth surface to study the effects of the cavity on the flow. The field of view was the same for both cases which made direct flow comparison possible. Flow characteristics such as the boundary layer profiles, Reynolds stress profiles and fluctuating velocity spectrum were studied over the cavity and at downstream locations to quantify the differences in the flows. The boundary layer profiles collapsed in the inner region of the boundary layer but there were small differences in the outer region. The Reynolds stress profiles were also very similar with differences within the uncertainties of processing the images and it reflected similar average behavior of the flow over a smooth wall and a Kevlar covered cavity. The fluctuating velocity spectrum studied over the cavity location showed some differences at low frequencies for all wall normal locations while at higher frequencies the differences were within ±3 dB. These measurements showcased the underlying physics behind the interaction of acoustic metamaterials and turbulent boundary layer flows creating possibilities of using these devices for flow control although further analysis/optimization is needed to fully understand the capabilities of these systems. The demonstration of no significant effect on flow by the Kevlar covered cavity stimulated development of sensors which can average over a region of the wall pressure spectrum. / M.S. / In the field of physics, acoustic metamaterials have gained popularity due to their ability to exhibit certain properties such as sound manipulation which cannot be seen in regular materials. These materials have a key feature which is the periodic arrangement of geometric elements in any dimension. These materials can support a phenomenon termed as acoustic surface waves which are essentially pressure disturbances in the medium which behave differently than some known phenomenon such as sound waves when excited by a broadband pressure signal in a stationary medium. Also, it has been shown that these materials can change the nature of the acoustic surface waves if their geometry is changed. Here a successful attempt has been made to link two different fields in physics: acoustic metamaterials (acoustics) and turbulent flows (fluid dynamics). The study here uses turbulent boundary layer flows to excite these metamaterials to show the existence of acoustic surface waves. This is done by creating an interface between the flow and the metamaterial using a Kevlar covered through cavity which is essentially a through hole connecting to different sides: flow side and the stationary air/quiescent side. This cavity acted as the source of excitation for the metamaterial. The Kevlar covering ensures that the flow does not get disturbed due to the cavity which was also proved in this study using a visualization technique: Particle Image Velocity (PIV). Two microphones were used to study the pressure field very close to two metamaterials; one was referred to as the slotted array comprised of slot cavities arranged in one dimension (along the direction of the flow), while the other was termed as the meander array and it comprised of a meandering channel. The pressure field was well characterized for both the acoustic metamaterials and it was proved that these metamaterials could support acoustic surface waves even when excited by a turbulent flow. The idea here was to fundamentally understand the interaction of acoustic metamaterials and turbulent flows, possibly finding use in applications such as trailing edge noise reduction. The use of these metamaterials in direct applications needs further investigation. A finding from the pressure field study showed that the pressure measured along the length of the Kevlar covered cavity was uniform. The flow visualization study looked at the turbulent flow on a smooth wall and over a Kevlar covered cavity. This was done by injecting tiny particles in air and shooting a laser sheet over these to illuminate the flow. Images were recorded using a high-speed camera to track the movement of these particles. It was found that the flow was unaffected with or without the presence of a Kevlar covered cavity. This result coupled with the pressure field uniformity could have some wide applications in the field of pressure sensing.

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

Wideband differential interferometry has been applied to the detection of SAW on specimen surfaces and ultrasonic compressional waves in liquids. Herein is described the performance of a wideband differential system which uses single mode optical fibers to transmit coherent light from input optics to a surface which supports which supports ultrasonic waves. Polarized light from a 2.0 mW helium-neon laser source is divided and coupled to two flexible bundled single mode optical fibers which transmit the light to a small remote detection head. The light at the output end of the fibers is collimated and focused by a varifocal lens system to points on the surface of a specimen to be inspected. Elastic waves on the specimen differentially modulate the relative phases of the two optical beams due to periodic changes in particle displacement at the surface. Upon reflection, the two beams are superimposed, filtered, and detected to produce an optical signal directly proportional to instantaneous displacements. Also described is the development of two beam and four beam differential systems for the detection of ultrasonic compressional waves in water. Two laser beams are transmitted through a water tank and combined to produce an interference pattern. The detected motion of the pattern yields a differential measure of the acoustic field amplitude at the location of the two probe beams. If a pulsed ultrasonic wave is generated in the tank in a direction perpendicular to and coplanar with the probe beams, each beam is modulated independently and output signals of opposite phase are produced. The acoustic sensitivity of both the above systems may be adjusted by changing the separation between the two spots on the surface or the two beams in the tank. The system effectively discriminates against low frequency noise vibrations, while the upper acoustic frequency response exceeds 100 MHz. Applications requiring flexibility allowed by a remote detection head can use the fiber system to their advantage while potential applications of the four beam system to three dimensional mapping and ultrasonic field scattering is suggested. / Master of Science