Negative group velocity of ultrasonic pulses in a bubbly liquid

Leary, Del M. (2001) Negative group velocity of ultrasonic pulses in a bubbly liquid. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (8MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

A wave pulse can propagate with a negative group velocity when it travels through a medium with anomalous dispersion, that is, when the derivative of the dispersion curve is negative. Here we report on the experimental observation of negative group velocities for pulses of ultrasound propagating ballistically through water containing gas bubbles. For frequencies near the resonant frequency of the bubbles, the absorption increases strongly and the group velocity becomes negative. Our experimental results are in good agreement with a theoretical model sound propagation in bubbly liquids if we assume a Gaussian distribution of bubble sizes.

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