Surface acoustic wave (SAW) devices are a solution for today’s ever growing need for passive wireless sensors. Orthogonal frequency coding (OFC) together with time division multiplexing (TDM) provides a large number of codes and coding algorithms producing devices that have excellent collision properties. Novel SAW noise-like re- flector (NLR) structures with pulse position modulation (PPM) are shown to exhibit good auto- and cross-correlation, and anti-collision properties. Multi-track, multi-transducer approaches yield devices with adjustable input impedances and enhanced collision properties for OFC TDM SAW sensor devices. Each track-transducer is designed for optimum performance for loss, coding, and chip reflectivity. Experimental results and theoretical predictions confirm a constant Q for SAW transducers for a given operational bandwidth, independent of device and transducer embodiment. Results on these new NLR SAW structures and devices along with a new novel 915 MHz transceiver based on a software radio approach was designed, built, and analyzed. Passive wireless SAW temperature sensors were interrogated and demodulated in a spread spectrum correlator system using a new adaptive filter. The first-ever SAW OFC four-sensor operation was demonstrated at a distance of 1 meter and a single sensor was shown to operate up to 3 meters. Comments on future work and directions are also presented

The concept of a compact sound source driven by piezoactuators is experimentally investigated, and analytical design tools are developed. The sound source, consisting of a thin, cylindrically curved aluminum panel and a pair of collocated, surface-bonded piezoceramic actuators, was developed with the objective of employing it as a secondary sound source in the active control of turbofan blade interaction inlet noise. The sound source was fitted in an experimental duct representative of an aircraft engine inlet, and the interior and exterior sound pressure levels generated by the source were measured. The effects of excitation voltage, excitation frequency, duct length, and downstream termination of the duct were investigated. It was found that the source is capable of generating relatively high acoustic levels at its fundamental frequency (over 130 dB at maximum voltage input). Techniques for analytically predicting the acoustic levels are investigated. A commercial code for numerical modeling of structural-acoustic radiation was utilized. Results show generally good agreement with experimental measurements for the case of the short duct. It is believed that the model accuracy can be further improved through additional refinements in the modeling techniques. / Master of Science

The monitoring of harmful ambient vapors is of major concern in the industrial environment. To this end, the development of systems which detect and respond in real time to specific vapors is a highly desirable goal. Surface Acoustic Wave (SAW) devices have been used for chemical analysis since 1978. While sensitive to mass changes occurring on their surfaces, they are not selective to the mass they will detect. Their use as chemical sensors requires the development of specificity for a vapor (or class of vapors) using selective chemical reagents suspended in film media that can have their permeability easily changed. This dissertation presents the development of an automated dosimeter for the detection of phosgene using SAW devices. By changing the film media from a very permeable material to a film exhibiting less permeability, the analytical range of the device using the same suspended selective chemical reagent is expanded to concentrations which the very permeable film is incapable of accurately measuring. / Ph. D.

An array of small, lightweight acoustic sources was investigated to determine how such an arrangement of sources would acoustically interact with a duct similar to that of a turbofan engine inlet. The sources were cylindrically curved aluminum panels excited in vibration by the application of a sinusoidally varying voltage to a piezoceramic actuator bonded to them. The finite element method was used as a design tool to size the panel based on desired vibration characteristics. A boundary element acoustic analysis was used to predict the acoustic output from various arrangements of sources. The central portion of the research was a series of experiments using an array of twelve sources arranged circumferentially in a duct. Measurements of the performance of each source revealed that the performance of the acoustic sources varied from source to source. This variation was assumed to have been caused by differences in the quality of the bond of each of the piezoceramic actuators to the panels. Directivity measurements were made in the far field. Measurements were also taken of the pressure field established in the duct cross-section. Modal decomposition was applied to the data. It was found that the dominant acoustic modes in the duct are those whose cut-on frequencies were near the frequency of excitation. / Master of Science

Micromachined gyroscopes are attractive replacements to conventional macro-mechanical and optical gyroscopes due to their small size, low power and low cost. The application domain of these devices is quickly expanding from automotive to aerospace and consumer electronics industries. As potential high volume consumer applications for micromachined gyroscopes continue to emerge, design and manufacturing techniques that improve their performance, shock survivability and reliability without driving up the cost and size become important. Today, state-of-the-art micromachined gyroscopes can achieve high performance with low frequency operation (3-30kHz) but at the cost of large form factor, large operating voltages and high vacuum packaging. At the same time, most consumer applications require gyroscopes with fast response time and high shock survivability, which are generally unavailable in low frequency gyroscopes. As a result, innovative designs and fabrication technologies that will offer more practical gyroscopes are desired. In this dissertation, capacitive bulk acoustic wave (BAW) silicon disk gyroscopes are introduced as a new class of micromachined gyroscope to investigate the operation of Coriolis-based vibratory gyroscopes at high frequency and further meet consumer electronics market demands. Capacitive BAW gyroscopes, operating in the frequency range of 1-10MHz are stationary devices with vibration amplitudes less than 20nm, resulting in high device bandwidth and high shock tolerance. They require low operating voltages, which simplifies the interface circuit design and implementation in standard CMOS technologies. They also demonstrate appropriate thermally stable performance in air, which eliminates the need both for vacuum packaging and for temperature control. A revised high aspect ratio poly- and single crystal silicon (HARPSS) process was utilized to implement these devices in thick SOI substrates with very small capacitive gap sizes (~200 nm). The prototype devices show ultra-high quality factors (Q>200,000) and large bandwidth of 15-30Hz. In addition, the design and implementation of BAW disk gyroscopes are optimized for self-matched mode operation. Operating a vibratory gyroscope in matched mode is a straightforward way to improve performance parameters but, is challenging to achieve without applying large voltages. In this work, self-matched mode operation was provided by enhanced design of the perforations of the disk structure. Furthermore, a multi-axis BAW gyroscope, an extension of the z-axis, is developed. This novel approach avoids the issues associated with integrating multiple proof masses, permitting a very small form factor. The multi-axis gyroscopes operate in out-of plane and in-plane modes to measure the rotation rate around the x- and z-axes. These gyroscopes were also optimized to achieve self-matched mode operation in their both modes.

The object of this thesis research was to develop and characterize a new type of acoustic biosensor - a ZnO-based laterally excited thickness shear mode (TSM) resonator in a solidly mounted configuration. The first specific aim of the research was to develop the theoretical underpinnings of the acoustic wave propagation in ZnO. Theoretical calculations were carried out by solving the piezoelectrically stiffened Christoffel equation to elucidate the acoustic modes that are excited through lateral excitation of a ZnO stack. A finite element model was developed to confirm the calculations and investigate the electric field orientation and density for various electrode configurations. A proof of concept study was also carried out using a Quartz Crystal Microbalance device to investigate the application of thickness shear mode resonators to cancer biomarker detection in complex media. The results helped to provide a firm foundation for the design of new gravimetric sensors with enhanced capabilities. The second specific aim was to design and fabricate arrays of multiple laterally excited TSM devices and fully characterize their electrical properties. The solidly mounted resonator configuration was developed for the ZnO-based devices through theoretical calculations and experimentation. A functional mirror comprised of W and SiO2 was implemented in development of the TSM resonators. The devices were fabricated and tested for values of interest such as Q, and electromechanical coupling (K2) as well as their ability to operate in liquids. The third specific aim was to investigate the optimal surface chemistry scheme for linking the antibody layer to the ZnO device surface. Crosslinking schemes involving organosilane molecules and a phosphonic acid were compared for immobilizing antibodies to the surface of the ZnO. Results indicate that the thiol-terminated organosilane provides high antibody surface coverage and uniformity and is an excellent candidate for planar ZnO functionalization. The fourth and final specific aim was to investigate the sensitivity of the acoustic immunosensors to potential diagnostic biomarkers. Initial tests were performed in buffer spiked with varying concentrations of the purified target antigen to develop a dose-response curve for the detection of mesothelin-rFc. Subsequent tests were carried out in prostate cancer cell line conditioned medium for the detection of PSA. The results of the experiments establish the operation of the devices in complex media, and indicate that the acoustic sensors are sensitive enough for the detection of biomolecular targets at clinically relevant concentrations.

The object of this research was to investigate dispersion in surface phononic crystals (PnCs) for application to a newly developed passive surface acoustic wave (SAW) ozone sensor. Frequency band gaps and slow sound already have been reported for PnC lattice structures. Such engineered structures are often advertised to reduce loss, increase sensitivity, and reduce device size. However, these advances have not yet been realized in the context of surface acoustic wave sensors. In early work, we computed SAW dispersion in patterned surface structures and we confirmed that our finite element computations of SAW dispersion in thin films and in one dimensional surface PnC structures agree with experimental results obtained by laser probe techniques. We analyzed the computations to guide device design in terms of sensitivity and joint spectral operating point. Next we conducted simulations and experiments to determine sensitivity and limit of detection for more conventional dispersive SAW devices and PnC sensors. Finally, we conducted extensive ozone detection trials on passive reflection mode SAW devices, using distinct components of the time dispersed response to compensate for the effect of temperature. The experimental work revealed that the devices may be used for dosimetry applications over periods of several days.

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.

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.