This thesis provides an analysis of an acoustic imaging technique using holography and the interaction of acoustic and light waves at a liquid-gas interface. Real time optical images of objects that have been transilluminated with ultrasonic waves in a liquid medium can be obtained. The liquid surface acts as a detector of the ultrasonic energy. When coherent light is reflected off the liquid surface an optical image of the object is obtained. An analysis is presented of the mechanisms involved including an analysis of the transient motion of the liquid surface. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The furnace exit gas temperature (FEGT) is one of the fundamental parameters necessary to determine the energy balance of the boiler in a coal-fired power plant, and is thus beneficial to the production of reliable thermo-fluid models of its operation and the operation of the systems down and upstream. The continuous measurement of the FEGT would also be a useful indicator to predict, prevent and diagnose faults, optimize boiler operation and aid the design of heat transfer surfaces. Acoustic pyrometry, a technique that measures temperature based on the travel time of an acoustic wave in a gas, is investigated as a viable solution for continuous direct measurement of the FEGT. This study focuses specifically on using acoustic pyrometry to reconstruct the temperature profile at the furnace exit including methods for accurately determining the time of flight (TOF) of acoustic waves. An improved reconstruction technique using radial basis functions (RBF) for interpolation and a least squares algorithm is simulated and its performance was compared to cubic spline interpolation, regression and Lagrange interpolation by evaluating its reconstruction accuracy in terms of mean and root-mean-squared (RMS) error when reconstructing set temperature profiles. Various parameters including transceiver positions, grid divisions and time of flight error, are investigated in terms of how they inform acoustic pyrometry implementation. The improved RBF interpolation function managed to reconstruct complex temperature profiles and had a greater reconstruction accuracy than compared interpolation methods, improving on the accuracy of previous work done. Random acoustic path error was found to not be additive with reconstruction error however repeating acoustic TOF readings improved reconstruction accuracy to mitigate this effect. In general, it was also found that symmetrical transmitter/receiver positions produced more accurate reconstructions as well as positioning receivers/transceivers and grid lines closer to the furnace walls, where the greatest temperature change occurs. In addition to testing reconstruction methods, a low-cost experimental set-up was constructed to measure the time of flight. The focus of this study was on using various signal processing methods to determine the time of flight and evaluating their accuracy in the presence of noise. Methods such as threshold detection with bandpass filtering, cross correlation, generalized cross-correlation (GCC) and a new method developed employing variable notch filters with locations and widths based on repetitive frequencies identified in the noise with cross correlation. The performance of methods was experimentally tested under varying signal to noise ratios (SNR) and noise conditions. These SNR tests showed that cross-correlation methods produced more reliable TOF readings under lower SNRs than threshold detection methods. Under white noise the smooth coherent transform (SCOT) GCC variation proved to produce the most accurate results producing an average TOF error of 0.84 % up until a SNR of 1.4 before reducing in accuracy. In coloured noise (generated based on previous boiler recordings) the variable notch filter method with crosscorrelation was able to identify repetitive noise frequencies filter them out and ultimately produced results with an average TOF error of 1.99 % up until a SNR of 0.67, where the noise level exceeds that of the signal.

Jet noise remains one of the most important problems in the aviation industry, and its reduction is sought in the context of both commercial and military aircraft. In this thesis, an investigation of the jet noise is conducted in terms of the effect of temperature and Mach number on low frequency acoustic spectra. A low-order model derived from the generalized acoustic analogy method via a lowrequency asymptotic approach is utilized, where the mean flow and pertinent statistical quantities are obtained from RANS simulations. The study involves a combination of seven acoustic Mach numbers ranging from 0.3 to 1.5 and five temperature ratios (TR) ranging from 1 to 3. The model is calibrated with existing experimental measurements of a Mach 0.9 and TR = 1 jet. The results show that the sound pressure level increases with the increase in Mach number, and decreases with the decrease in temperature ratios.

Studies were conducted to establish a new technique for predicting moisture content (MC) of soybean using acoustic methodology including the development of a technique for determining the variety of soybean based on dimensional measurements. The first objective of this study is to investigate a more detailed frequency domain method of modelling the MC of four varieties of soybean: Asgrow AG5701, Delta Pine DP5915RR, Hutcheson Public, and Pioneer 95B53. Seven different levels of MC for each variety between 7% and 18% were examined using an impact chamber as the means of producing the acoustical energy. The time domain data collected by a data recorder were transformed into frequency domain and the power spectral density (PSD) was computed based on a 1024-point Fast Fourier Transform (FFT). The frequency range of the data was from 0 Hz to 8000 Hz. The frequency domain data were partitioned into multiple slices of frequency bands (sub bands), and the total energy of each sub band was computed to yield a data point and the resulting data point was normalized by dividing it by the data point from a selected slice of frequency band (reference frequency band). Statistical analyses were used to develop the models using multiple regressions. In order to facilitate the use of variety specific MC model, this study also includes dimensional measurements of the four varieties of soybean to determine whether or not it is possible to discriminate a soybean variety based on its dimensional features. The dimensional measurements were done with a dial caliper in three axes: parallel to the Hylo (d1), perpendicular to the Hylo (d2), and in the same plane as the Hylo (d3). One hundred grains of each variety of soybeans were used in the measurements.

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Thesis (Ph. D.)--Ohio State University, 2007. / Full text release at OhioLINK's ETD Center delayed at author's request

The OFDM technology has been extensively used in many radio communicationtechnologies. For example, OFDM is the core technology applied in WiFi, WiMAXand LTE. Its main advantages include high bandwidth utilization, strong noise im-munity and the capability to resist frequency selective fading. However, OFDMtechnology is not only applied in the field of radio communication, but has alsobeen developed greatly in acoustic communication, namely the so called acousticOFDM. Thanks to the acoustic OFDM technology, the information can be em-bedded in audio and then transmitted so that the receiver can obtain the requiredinformation through certain demodulation mechanisms without severely affectingthe audio quality.This thesis mainly discusses how to embed and transmit information in audioby making use of acoustic OFDM. Based on the theoretical systematic structure, italso designs a simulation system and a measurement system respectively. In thesetwo systems, channel coding, manners of modulation and demodulation, timingsynchronization and parameters of the functional components are configured in themost reasonable way in order to achieve relatively strong stability and robustnessof the system. Moreover, power control and the compatibility between audio andOFDM signals are also explained and analyzed in this thesis.Based on the experimental results, the author analyzes the performance of thesystem and the factors that affect the performance of the system, such as the typeof audio, distance between transmitter and receiver, audio output level and so on.According to this analysis, it is proved that the simulation system can work steadilyin any audio of wav format and transmit information correctly. However, dueto the hardware limitations of the receiver and sender devices, the measurementsystem is unstable to a certain degree. Finally, this thesis draws conclusions of theresearch results and points out unsolved problems in the experiments. Eventually,some expectations for this research orientation are stated and relevant suggestionsare proposed.

Acoustic wave fields in an ocean waveguide with a sediment layer having continuously varying density and sound speed overlying an elastic subbottom is considered in this analysis. The objective of this study is to investigate the effects of seabed acoustic properties,including the density and sound speed of sediment layer and subbottom, on the characteristics of the wave fields. This geometry offers a good environmental model which closely resembles a realistic ocean waveguide. This noise model was first proposed by Kuperman and Ingenito in the study of surface-generated ambient noise using normal mode approach.Recent experimental data provided by Hamilton have shown that the sediment layer in the seabed experiences a transitional change in which the density and the sound speed vary continuously from one value at the top to another at the bottom of the layer. Traditionally, in treating wave propagation in a such environment,the medium is represented by a series of layers,each of which has a uniform property within the layer.While this approximation may reasonably describe the variations of the medium as a whole,the details of the acoustic constituent may only be seen when these variations are properly accounted for. Moreover, the subbottom is taken to be a uniform elastic medium that is capable of supporting both compressional and shear waves. For the study of reflection from seabed, various kinds of sound speed and density profiles are employed.The wavenumber spectrum has clearly shown the various kinds wave components in the waveguide,in particular, the Scholte wave mode.The noise intensity in the water column is dominated by the modal and continuous spectrum.For the set of parameters chosen,the horizontal correlation lengths of the noise field tend to increase as the noise sources becomes more correlated, however, the vertical correlation tends to reduce. This indicates that the coherency of the noise field is controlled both by the noise sources and waveguide properties.

Thesis (M. Aud.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (leaves 132-149). Also available via the World Wide Web.