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Please use this identifier to cite or link to this item: http://www.lib.ncsu.edu/resolver/1840.16/2769

Title: Nonlinear Acoustic Characterization of Targets
Authors: Garner, Glenwood, III
Advisors: Wesley Snyder, Committee Member
Michael Steer, Committee Co-Chair
Hamid Krim, Committee Chair
Keywords: acoustic imaging
acoustic measurements
acoustic parametric devices
nonlinear acoustics
Issue Date: 8-Apr-2008
Degree: MS
Discipline: Electrical Engineering
Abstract: Recent techniques in nonlinear vibro-acoustics have demonstrated improved sensing capabilities for landmine detection. These methods however, place the transmit and⁄or receive devices extremely close to a potentially dangerous target. This paper discusses a novel approach where ultrasonic parametric arrays are used to achieve excitation at standoff ranges in air. When two frequencies, f1 and f2 are directed to excite a target, the nonlinear response consists of sum and difference frequencies. The difference frequency may be carefully swept to produce an acoustic signature of the target, reflecting its size and density information. As part of this research, a more accurate third order nonlinear ultrasonic propagation model is developed to analyze signal strength and frequency at the target. Due to the inefficient mixing of the ultrasonic tones, reflected signals have very small amplitude. This thesis develops high-resolution spectral analysis techniques (e.g. multiple signal classification (MUSIC) algorithm) to extract particularly weak signals (in low signal to noise ratio scenario) and thus substantially improve target characteristics estimation performance and provides a viable and practical approach to perform acoustic imaging. Experimental results demonstrate for the first time, a capacity to remotely classify a hollow target from a solid one, with resonance patterns predicting the approximate size of the target.
URI: http://www.lib.ncsu.edu/resolver/1840.16/2769
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