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Updated: Jul 11, 2026

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Published on: May 9, 2021
Ultrasonic properties of a suspension of microspheres supporting negative group velocities
Joel Mobley1, Robert Evans Heithaus
1Department of Physics and Astronomy, and National Center for Physical Acoustics, University of Mississippi, University, Mississippi 38677, USA. jmobley@olemiss.edu
Abstract:
The ultrasonic attenuation coefficient, phase velocity, and group velocity spectra are reported for a suspension that supports negative group velocities. The suspension consists of plastic microspheres with an average radius of 80 microm in an aqueous medium at a volume fraction of 3%. The spectra are measured using a broadband method covering a range from 2 to 20 MHz. The suspension exhibits negative group delays over a band near 4.5 MHz, with the group velocity magnitude exceeding 4.3 x 10(8) m/s at one point. The causal consistency of these results is confirmed using Kramers-Kronig relations.
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