Using Long Kasami Sequences for Acoustic Scatterer Identification and Object Imaging

Date
2015-04-30
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Abstract
Acoustic image acquisition is a trade off between many factors including available signal power, allowable signal power, medium bandwidth and image frame rate. Excitation signals derived from short codes or modulated pulses is an area of much research to improve performance. This thesis focuses on the use of long Kasami transmit sequences to identify scatterer parameters and locate heterogeneities. The use of long sequences provides a means of increasing signal-to-noise ratio despite a fixed amount of transmit power. This thesis makes a contribution in a few areas related to the acoustic imaging problem. The core innovation of the work develops and verifies the use of a continuous illuminating acoustic beam in contrast to short high energy pulses for the recovery of the locations of scatterers normally undetectable with shorter excitations of the same amplitude. Secondary to the main proposal, concurrent transmitting and receiving of multiple scanlines in the same environment is achieved by employing pseudo-random sequences with optimal orthogonality from the Kasami set such that multiple independent scanlines are decorrelated and recovered. Another auxiliary benefit is parameter identification from demodulated in-phase and quadrature versions of the recovered sequences. These provide linearly independent information related to velocity and density parameters of scatteres. The core concept and its accessories are implemented with a low cost, commercially available architecture. The approach used in this thesis starts with the development of an analytical model that relates the cross-correlation result of long pseudo-random sequences and recovered information to locations and physical parameter values. The concept is demonstrated with Kasami sequences in simulation and with laboratory experiments. Results show that long Kasami transmit sequences, even if sustained indefinitely, recover the density and wave velocity values of scatterers, and detect internal interfaces of objects despite interference from foreign, concurrent imaging beams.
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Keywords
Engineering--Electronics and Electrical
Citation
Leskiw, C. (2015). Using Long Kasami Sequences for Acoustic Scatterer Identification and Object Imaging (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/28618