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1	Nonlinear Acoustics Applied to NonDestructive Testing / Olinjär akustik applicerad på oförstörande provning Haller, Kristian January 2007 (has links) Sensitive nonlinear acoustic methods are suitable for material characterization. This thesis describes three nonlinear acoustic methods that are proven useful for detection of defects like cracks and delaminations in solids. They offer the possibility to use relatively low frequencies which is advantageous because attenuation and diffraction effects are smaller for low frequencies. Therefore large and multi-layered complete objects can be investigated in about one second. Sometimes the position of the damage is required. But it is in general difficult to limit the geometrical extent of low-frequency acoustic waves. A technique is presented that constrains the wave field to a localized trapped mode so that damage can be located. nonlinear acoustics nondestructive testing activation density slow dynamics resonance frequency nonlinear wave modulation spectroscopy harmonic generation trapped modes open resonator sweep rate