Sound beyond the speed of light: Measurement of negative group velocity in an acoustic loop filter

W. M. Robertson, J. Pappafotis, P. Flannigan, J. Cathey, B. Cathey, C. Klaus

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44 Scopus citations

Abstract

The authors describe the experimental observation of negative group velocity propagation of sound waves through an asymmetric loop filter. The characteristics of the filter are established using impulse response and direct tunneling of narrow bandwidth Gaussian pulses. The results confirm recent theoretical predictions that faster-than-light group velocity propagation of sound is possible. Further, the results show that the spectral rephasing achieved in a loop filter is sufficient to produce negative group velocities independent of the phase velocity of the spectral components themselves. Thus, superluminal propagation is realized despite almost six orders of magnitude difference between the speeds of sound and light.

Original languageEnglish
Article number014102
JournalApplied Physics Letters
Volume90
Issue number1
DOIs
StatePublished - 2007
Externally publishedYes

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