Simple, cheap and reliable echo-based ultrasonic ranging systems such as the Polaroid ranging unit are easily applied to indoor applications. However, to measure the range between an unmanned helicopter and a moving ship deck at sea using ultrasound requires a more robust ranging system, because rushing air and breaking water are known ultrasound noise sources. The work of designing, constructing and testing such a system is described in this dissertation. The compact, UAV ready ultrasound transmitter module provides high power, broadband arbitrary signal generation. The separate field-ready receiver is based on a modern embedded Digital Signal Processor (DSP), providing high speed matched-filter correlation processing. Large time-bandwidth signalling is employed to maximise the signal to noise ratio of the ranging system. Synthesised experiments demonstrate the ability of the correlation processing to reliably recover timing from signals buried in noise. Real world experiments demonstrate decimetre accuracy with two centimetre resolution, ten metre range and 32Hz refresh rate. A maximum boresight range of up to 38m is supported.

Thesis (Ph. D.)--Worcester Polytechnic Institute. / Keywords: grid generated turbulence; wave propagation; acoustics; ultrasonic flowmetering. Includes bibliographical references (p. 109-116).

The field of restorative dentistry and the problem of ultrasonic airframe corrosion in aerospace are introduced as motivation for the construction of a miniature ultrasonic pulser/receiver. / A broadly applicable ultrasonic pulser and receiver system is developed. Two pulsers, a 5V square and a 100V spike, and a 52dB amplifier with a 57MHz 6dB bandwidth were constructed as a result. These battery powered devices are tailored for compatibility with a custom built wireless data transmission system, also driven by the same voltage. It is demonstrated that the new pulser/receiver is comparable to the commercial system in performance in certain areas. / The new pulsers/receiver and a commercial one are used in this work. The data is acquired and analyzed using LabView and Matlab. It is shown that the ultrasonic technique can be used to follow the reaction in time as well as to gauge the cure of dental composites. The current work in ultrasonic airframe corrosion detection is furthered and the wireless system's functionality is affirmed.

Thèse (M.Eng.) -- Université du Québec à Chicoutimi, 2005. / La p. de t. porte en outre: Mémoire présenté à l'Université du Québec à Chicoutimi comme exigence partielle de la maîtrise en ingénierie. CaQCU Bibliogr.: f. 138-144. Document électronique également accessible en format PDF. CaQCU

Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Jacobs, Laurence J.; Committee Co-Chair: Wang, Yang; Committee Member: Kim, Jin-Yeon. Part of the SMARTech Electronic Thesis and Dissertation Collection.

No description available.

The state of cure of epoxies is an important issue in the manufacture of graphite epoxy composites used in aerospace structures. Variations in the initial state and process used to cure the epoxy resin in a composite material lead to variations in the mechanical properties of the part manufactured from the composite._[12] Control of these variation can be accomplished by monitoring the bulk and shear moduli of the epoxy resin as it cures. The moduli properties of the resin determine the acoustic properties of the epoxy._{[12],[13],[14]} Hence measurement of the acoustic longitudinal velocity and attenuation of the epoxy during its cure cycle provides a good indicator of the state of cure. Optical fiber waveguides can be embedded within a host material and used to detect longitudinal acoustic waves._[15],[16] Herein, the mechanisms allowing the detection of ultrasound with optical fiber are presented. An analysis of optical fiber waveguides and optical fiber based interferometric detection methods is performed in detail. The interaction of radial strain fields, induced by longitudinal acoustic waves, with singlemode optical fibers is described. Experimental results obtained in epoxy cure monitoring, using an optical fiber based method for acoustic detection, are compared with results obtained using conventional piezoelectric based acoustic detection methods. / Master of Science

"The present study utilizes the ultrasonic travel-time technique to diagnose grid-generated turbulence. The statistics of the travel-time variations of ultrasonic wave propagation along a path are used to determine some metrics of the turbulence. The motivation for this work stems from the observation of substantial delta-t variation in ultrasonic measuring devices like flow meters and circulation meters. Typically, averaging can be used to extract mean values from such time series. The corollary is that the fluctuations contain information about the turbulence. Experimental data were obtained for ultrasonic wave propagation downstream of a heated grid in a wind tunnel. Such grid-generated turbulence is well characterized and features a mean flow with superimposed velocity and temperature fluctuations. The ultrasonic path could be perpendicular or oblique to the mean flow direction. Path lengths were of the order of 0.3 m and the transducers were of 100 kHz working frequency. The data acquisition and control system featured a very high-speed analog to digital conversion card that enabled excellent resolution of ultrasonic signals. Experimental data for the travel-time variance were validated using ray acoustic theory along with the Kolmogorov “2/3” law. It is demonstrated that the ultrasonic technique, together with theoretical models, provides a basis for turbulent flow diagnostics. As a result, the structure constant appearing in the Kolmogorov “2/3” law is determined based on the experimental data. The effect of turbulence on acoustic waves, in terms of the travel time, was studied for various mean velocities and for different angular orientations of the acoustic waves with respect to the mean flow. Average travel time in the presence of turbulence was shorter then in the undisturbed media. The effect of the time shift between the travel times in turbulent and undisturbed media is associated with Fermat’s principle. The travel time and log-amplitude variance of acoustic waves were investigated as functions of travel distance and mean velocity over a range of Reynolds number varying from 4000 to 20000. Experimental data are interpreted using classical ray acoustic approach and the parabolic acoustic equation approach together with the perturbation method. It was experimentally demonstrated that there is a strong dependence of the travel time on the mean velocity even in the case where the propagation of acoustic waves is perpendicular to the mean velocity. The effect of thermal fluctuations, which result in fluctuations of sound speed, was studied for two temperatures of the grid: (no grid heating) and . A semi analytical acoustic propagation model that allows determination of the spacial correlation functions of flow field is developed based on the classical flow meter equation and statistics of the travel time of acoustic waves traveling through the velocity and the thermal turbulence. The basic flow meter equation is reconsidered in order to take into account sound speed fluctuations and turbulent velocity. The resulting equation is written in terms of correlation functions of travel time, sound speed fluctuation and turbulent velocity fluctuations. Experimentally measured travel time statistics data with and without grid heating are approximated by Gaussian function and used to solve the integral flow meter equation in terms of correlation functions analytically."

The focus of this Ph.D. thesis research is a new piezoelectrically driven micromachined ultrasonic atomizer concept that utilizes fluid cavity resonances in the 15 MHz range along with acoustic wave focusing to generate the pressure gradient required for droplet or jet ejection. This ejection technique exhibits low-power operation while addressing the key challenges associated with other atomization technologies including production of sub-5 um diameter droplets, low-temperature operation, the capacity to scale throughput up or down, and simple, low-cost fabrication. This thesis research includes device development and fabrication as well as experimental characterization and theoretical modeling of the acoustics and fluid mechanics underlying device operation. The main goal is to gain an understanding of the fundamental physics of these processes in order to achieve optimal design and controlled operation of the atomizer. Simulations of the acoustic response of the system for various device geometries and different ejection fluid properties predict the resonant frequencies of the device and confirm that pressure field focusing occurs. High-spatial-resolution stroboscopic visualization of fluid ejection under various operating conditions is used to investigate whether the proposed atomizer is capable of operating in either the discrete-droplet or continuous-jet mode. The results of the visualization experiments combined with a scaling analysis provide a basic understanding of the physics governing the ejection process and allow for the establishment of simple scaling laws that prescribe the mode (e.g., discrete-droplet vs. continuous-jet) of ejection. In parallel, a detailed computational fluid dynamics (CFD) analysis of the fluid interface evolution and droplet formation and transport during the ejection process provides in-depth insight into the physics of the ejection process and determines the limits of validity of the scaling laws. These characterization efforts performed in concert with device development lead to the optimal device design. The unique advantages enabled by the developed micromachined ultrasonic atomizer are illustrated for challenging fluid atomization examples from a variety of applications ranging from fuel processing on small scales to ultra-soft electrospray ionization of biomolecules for bioanalytical mass spectrometry.

This research investigates how ultrasonic damage monitoring in civil structures can be implemented on a small, battery-powered, self-contained device. The device is intended for the continuous monitoring of surface breaking cracks in steel using Rayleigh waves. This study in detail presents the challenges that are to be considered for the intended ultrasonic monitoring, with the objective to provide a foundation for the future development of a fully autonomously operating device. The study proposes a suitable hardware and software layout, and a prototype device is built using a digital signal processor, a commercial wireless transceiver, and custom amplification circuits. With the help of two narrowband ultrasonic contact transducers in a pitch-catch setup and appropriate contact wedges, the wave field that arises from scattering of an incident tone burst wave at a crack is measured. A data analysis algorithm extracts wave burst signals from the acquired output in order to minimize the data that is to be transmitted. Additional compression of the data and the implementation of a communication protocol allow for a reliable and efficient wireless transmission. In order to demonstrate the feasibility of the proposed approach, measurements of notches in a steel plate with different depths are taken. Measurement results from experiments with commercial ultrasonic equipment are compared to measurements taken with the prototype device. The influence of the sampling distortions on the signals are analyzed. The scope of this study is limited to a qualitative analysis of the experimental results; quantitative methods to determine the dimensions of a crack or notch from the measured data are not included. The research conducted demonstrates that taking ultrasonic measurements with a small, self-contained device is feasible. Comparison of frequency-based to time-based signal analysis methods yields that frequency-based methods are preferable, as they are affected less by sampling effects. The experimental results show that the intended ultrasonic examination technique can be used for qualitative damage assessment. The knowledge gained in this study contributes to improving the safety of civil infrastructure. Continuous local damage monitoring as proposed helps to detect critical conditions in-time, and to take countermeasures to avoid catastrophic failures.