<p>In this thesis, we develop methods for addressing the deficiencies of array processing with linear thinned arrays. Our methods are designed for array systems mounted on moving platforms and exploit synthetic aperture processing techniques. In particular, we use array motion to decrease the sidelobe levels and increase the degrees of freedom available from thinned array systems. In this work, we consider two application areas 1) passive SONAR and 2) ultrasound imaging. </p><p>Synthetic aperture processing is a methodology for exploiting array motion and has been successfully used in practice to increase array resolution. By spatially sampling along the path of the array virtual sensors can be realized and coherently fused to the existing array. The novel contribution of this work is our application of synthetic aperture processing. Here our goal is not to increase array resolution, instead we propose to use the synthetic aperture process to expand the spatial covariance and spatial frequency sensing capabilities of thinned array system.</p><p> </p><p>In the passive sensing case, we use a class of thinned arrays know as co-prime linear sensor arrays for source localization. The class of co-prime arrays provides roughly half the aperture worth of spatial covariances and with modest array motion can be extended to the full aperture of the array. The amount of motion required to produce a full set of spatial covariances is shown to be a function of the co-prime array parameters and is only a fraction of the total aperture of the array. The full set of spatial covariances can be used to form a spatial covariance matrix with dimension equal to that of a uniform array. With a spatial covariance matrix in hand one can perform signal processing tasks as if the array were fully populated. Three methods for spatial covariance matrix estimation are compared in different source localization scenarios. In the work presented here, we demonstrate the benefits of our approach for achieving reduced sidelobe levels and extending the source localization capabilities above the limits of the static co-prime array. </p><p>In the active sensing case, we develop a framework for incorporating motion using thinned arrays for ultrasound imaging. In this setting, array motion is used to augment the spatial frequency sensing capabilities of the thinned array system. Here we develop an augmentation strategy based on using quarter-wavelength array translations to fill-in missing spatial frequencies not measured by the static thinned array. The quarter-wavelength translation enables the thinned array system to sample missing spatial frequencies and increase the redundancy of other spatial frequencies sampled by the array. We compare the level of redundancy in sampling the spatial frequencies achieved by the thinned arrays post translation to different levels of sample redundancy derived from pruning the transmit/receive events of a uniform array. In this manner, we are able to examine how the level of spatial frequency redundancy afforded by different thinned arrays compare over the full redundancy range of the uniform array. While artificially pruning the uniform array does not necessarily create realizable arrays, it provides the means to compare image quality at different spatial frequency redundancy levels. In this work, we are able to conclude that images formed from thinned arrays using the translated synthetic aperture process are capable of approximating images formed from the corresponding uniform array. In particular, the systems considered in this work have approximately one-third of the active sensors when compared to the uniform array. </p><p>In both application areas, the use of thinned arrays offers a reduction in the cost to deploy and maintain a given array system. The feature that makes it possible to overcome the spatial sampling deficiencies of thinned array systems is motion and it is at the core of the performance gains in these applications.</p> / Dissertation

Submitted by Maicon Juliano Schmidt (maicons) on 2015-07-06T18:20:56Z No. of bitstreams: 1 Lucas Adams Seewald.pdf: 2650183 bytes, checksum: b48d406145d4e90aaf15d30b38b2ccbc (MD5) / Made available in DSpace on 2015-07-06T18:20:56Z (GMT). No. of bitstreams: 1 Lucas Adams Seewald.pdf: 2650183 bytes, checksum: b48d406145d4e90aaf15d30b38b2ccbc (MD5) Previous issue date: 2014-01-31 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares / Este documento apresenta uma avaliação de aplicabilidade do Kinect em conjunto com o SPR-PHAT como solução de Localização de Fonte Sonora. Um protótipo capaz de se comunicar com o aparelho e executar SRP-PHAT foi implementado com a finalidade de testar a precisão da solução. É realizada uma revisão dos fundamentos da Localização de Fonte Sonora e seus princípios matemáticos, com foco específico no SRP-PHAT. Seguindo para o Kinect, são realizadas algumas considerações a respeito de seus componentes e limitações. São apresentados alguns trabalhos que recorrem ao aparelho para localizar fontes sonoras, seguidos de resultados de precisão do SRP-PHAT obtidos por diferentes autores. Foram realizados dois grupos de experimentos, um voltado para as características da fonte sonora e o outro para a qualidade da solução proposta. Os experimentos incluem localização em duas e três dimensões, utilizando dois Kinects no segundo caso. As particularidades de implementação do programa que manipula os Kinects e executa o algoritmo de localização são fornecidas juntamente com descrições dos procedimentos de teste adotados. Os resultados apresentados mostram que a solução é capaz de apontar com precisão para a direção da fonte. / This document presents an evaluation of Kinect together with SRP-PHAT as a Sound Source Localization solution. A functional prototype able to communicate with the device and perform SRP-PHAT was implemented in order to test the solution’s accuracy. The fundamentals of Sound Source Localization and it’s mathematical principles are reviewed, focusing specifically on the SRP-PHAT. Moving on to the Kinect device, some considerations are made about it’s components and limitations. Related work which resources to Kinects source localization capabilities is presented, followed by SRP-PHAT precision test results attained by different authors. Two experimental sets were conducted, one focused on the source signal properties and the other on measuring the proposed solutions quality. Performed experiments comprehend two dimensional and three dimensional localization, being a second Kinect needed for the latter. Implementation aspects concerning the software responsible for manipulating both Kinects and executing the localization algorithm are described along with experimental procedure details. Presented results show that the proposed solution can accurately point at the sources direction.

There has always been a desire to apply technology to human endeavors to increase a person's capabilities and reduce the numbers or skill level required of the people involved, or replace the people altogether. Three fundamental areas are investigated where technology can enable the reduction or removal of humans in complex tasks. The fi rst area of research is the rapid calibration of multiple camera systems when cameras share an overlapping fi eld of view allowing for 3D computer vision applications. A simple method for the rapid calibration of such systems is introduced. The second area of research is the autonomous exploration of hallways or other urbancanyon environments in the absence of a global positions system (GPS) using only an inertial motion unit (IMU) and a monocular camera. Desired paths that generate accurate vehicle state estimates for simple ground vehicles are identi fied and the bene fits of integrated estimation and control are investigated. It is demonstrated that considering estimation accuracy is essential to produce efficient guidance and control. The Schmidt-Kalman filter is applied to the vision-aided inertial navigation system in a novel manner, reducing the state vector size signi ficantly. The final area of research is a decentralized swarm based approach to source localization using a high fidelity environment model to directly provide vehicle updates. The approach is an extension of a standard quadratic model that provides linear updates. The new approach leverages information from the higher-order terms of the environment model showing dramatic improvement over the standard method.

The study is based on the acoustic data collected by horizontal line array (HLA) of Asian Seas International Acoustic Experiment (ASIAEX) in South China Sea of 2001. Beamforming was used to localize the sound sources during the experiment, such as explosive, to understand its correlation with position deviation from the array. According to previous studies, the horizontal line array has ambiguity in bearing identification, which was often resolved by maneuvering array¡¦s position, therefore it can also be concluded that the well understanding of array¡¦s position is the key to the accurate source localization. Due to the limitation of element spacing of array used in the experiment, 50 Hz is the highest frequency can be analyzed in the study, so the recorded explosive sounds were chosen for analysis. The numerical test of array has shown the width of main lobe in beamforming is reduced by the increasing total length of the array, and the energy in the side lobes would affect the accuracy of source bearing. During the experiment, the horizontal array was found, and proved indirectly by current measurement of acoustic Dopper current profiler, to be moved by tidal currents, so the deviation from the designed deploy position can be computed. The deviation was used to quantify the resolution effect on localization by the movement of array, and when there is a 10 m deviation, the width of main lobe would increase from 8¢X to 16¢X in the studied case. The experimental results match the simulations well, so it can provide a guideline in predicting the accuracy of underwater source localization when the movement of horizontal line array is possible. Key word: underwater source localization, horizontal line array, beamforming, position deviation, array resolution

People are usually directed towards each other in conversations, to make it easier to hear what is being said. Algorithms for voice and speech recognition works in a similar way, regarding the microphone direction towards the sound source. In this thesis in electronics has therefore a servo control with binaural sound localization been implemented on a microcontroller connected to two microphones. When people perceive sound, the brain can estimate the sound source direction by comparing the time taken by the sound reaching one ear to the other [1]. The difference in time is called the interaural time difference, and can be calculated using various techniques. An exploratory comparison between the techniques cross-correlation and cross-spectrum analysis was carried out before implementation. Advantages and disadvantages of each technique were evaluated at the same time. The result is a functioning servo control, that uses a cross correlation algorithm to calculate the interaural time difference, and controls a servo motor towards the sound source with a P-regulated error reduction method. The project was implemented on the microcontroller ATmega328P from Atmel without using floating point calculations. The thesis was carried out on behalf of the company Jetspark Robotics.

Constant False Alarm Rate (CFAR) Processors are important for applications where thousands of detection tests are made per second, such as in radar. This thesis introduces a new method for CFAR threshold estimation that is particularly applicable to sound source detection with distributed microphone systems. The novel CFAR Processor exploits the near symmetry about 0 for the acoustic pixel values created by steered-response coherent power in conjunction with a partial whitening preprocessor to estimate thresholds for positive values, which represent potential targets. To remove the low frequency components responsible for degrading CFAR performance, fixed and adaptive high-pass filters are applied. A relation is proposed and it tested the minimum high-pass cut-off frequency and the microphone geometry. Experimental results for linear, perimeter and planar arrays illustrate that for desired false alarm (FA) probabilities ranging from 10-1 and 10-6, a good CFAR performance can be achieved by modeling the coherent power with Chi-square and Weibull distributions and the ratio of desired over experimental FA probabilities can be limited within an order of magnitude.

This thesis presents a method for a small, inexpensive mobile robot equipped with a single high resolution scintillation detector to quickly survey an area and convey information about local sources of gamma radiation to a remote human operator. This is achieved by surrounding the detector with a lead sheath that blocks all gamma rays except those incident along the detector???s axial direction. A horizontal scan is performed by rotating the detector and a directional profile of gamma radiation is constructed. In addition a visual panorama of the local area is assembled using a camera mounted on the detector. A plot of the detector signal versus angle is then overlaid on top of the visual panorama and visible peaks clearly indicate the direction of local gamma radiation sources. Moreover, measuring the energy spectrum of gamma rays in each direction produces a 2D count frequency histogram where distinct peaks indicate the energy and direction of local gamma ray sources allowing the identification of different radio-isotopes.

Bilateral implantation of a cochlear implant (CI) after a >2 year period of unilateral hearing with a second implant has been shown to result in altered latencies in brainstem responses in children with congenital deafness. In this thesis, a neural source localization method was developed to investigate the effects of unilateral CI use on cortical development after the implantation of a 2nd CI. The electroencephalography (EEG) source localization method is based on the linearly constrained minimum variance (LCMV) vector beamformer and utilizes null constraints to minimize the electrical artifact produced by the CI. The accuracy of the method was assessed and optimized through simulations and comparisons to beamforming with magnetoencephalography (MEG) data. After using cluster analyses to ensure that sources compared across subjects originate from the same neural generators, a study was done to examine the effects of unilateral CI hearing on hemispheric lateralization to monaural responses. It was found that a >2 year period of unilateral hearing results in expanded projections from the 1st implanted ear to the contralateral auditory area that is not reversed by implantation of a 2nd CI. A subsequent study was performed to examine the effects of unilateral CI hearing on the contributions of the 1st and 2nd implanted ears to the binaural response. It was found that in children with > 2 years of unilateral hearing, the binaural response is dominated by the 1st implanted ear. Together, these results suggest that the delay between the 1st and 2nd CI should be minimized in bilateral implantation to avoid dominance of auditory pathways from the 1st implanted ear. This dominance limits developmental competition from the 2nd CI and potentially contributes to poorer performance in speech detection in noise tasks.

Bilateral implantation of a cochlear implant (CI) after a >2 year period of unilateral hearing with a second implant has been shown to result in altered latencies in brainstem responses in children with congenital deafness. In this thesis, a neural source localization method was developed to investigate the effects of unilateral CI use on cortical development after the implantation of a 2nd CI. The electroencephalography (EEG) source localization method is based on the linearly constrained minimum variance (LCMV) vector beamformer and utilizes null constraints to minimize the electrical artifact produced by the CI. The accuracy of the method was assessed and optimized through simulations and comparisons to beamforming with magnetoencephalography (MEG) data. After using cluster analyses to ensure that sources compared across subjects originate from the same neural generators, a study was done to examine the effects of unilateral CI hearing on hemispheric lateralization to monaural responses. It was found that a >2 year period of unilateral hearing results in expanded projections from the 1st implanted ear to the contralateral auditory area that is not reversed by implantation of a 2nd CI. A subsequent study was performed to examine the effects of unilateral CI hearing on the contributions of the 1st and 2nd implanted ears to the binaural response. It was found that in children with > 2 years of unilateral hearing, the binaural response is dominated by the 1st implanted ear. Together, these results suggest that the delay between the 1st and 2nd CI should be minimized in bilateral implantation to avoid dominance of auditory pathways from the 1st implanted ear. This dominance limits developmental competition from the 2nd CI and potentially contributes to poorer performance in speech detection in noise tasks.

Currently there does not exist a type of peripheral nerve interface that adequately combines spatial selectivity, spatial coverage and low invasiveness. In order to address this lack, we investigated the application of bioelectric source localization algorithms, adapted from electroencephalography/magnetoencephalography, to recordings from a 56-contact “matrix” nerve cuff electrode. If successful, this strategy would enable us to improve current neuroprostheses and conduct more detailed investigations of neural control systems. Using forward field similarities, we first developed a method to reduce the number of unnecessary variables in the inverse problem, and in doing so obtained an upper bound on the spatial resolution. Next, a simulation study of the peripheral nerve source localization problem revealed that the method is unlikely to work unless noise is very low and a very accurate model of the nerve is available. Under more realistic conditions, the method had localization errors in the 140 μm-180 μm range, high numbers of spurious pathways, and low resolution. On the other hand, the simulations also showed that imposing physiologically meaningful constraints on the solution can reduce the number of spurious pathways. Both the influence of the constraints and the importance of the model accuracy were validated experimentally using recordings from rat sciatic nerves. Unfortunately, neither idealized models nor models based on nerve sample cross-sections were sufficiently accurate to allow reliable identification of the branches stimulated during the experiments. To overcome this problem, an experimental leadfield was constructed using training data, thereby eliminating the dependence on anatomical models. This new strategy was successful in identifying single-branch cases, but not multi-branches ones. Lastly, an examination of the information contained in the matrix cuff recordings was performed in comparison to a single-ring configuration of contacts. The matrix cuff was able to achieve better fascicle discrimination due to its ability to select among the most informative locations around the nerve. These findings suggest that nerve cuff-based neuroprosthetic applications would benefit from implanting devices with a large number of contacts, then performing a contact selection procedure. Conditions that must be met before source localization approaches can be applied in practice to peripheral nerves were also discussed.