Blowing out a candle from a distance with high amplitude time reversal

Abstract

Time reversal is a technique that allows the focusing of sound from a source to a remote location causing an impulsive focusing event. Using more sources and other amplitude-increasing techniques, the focusing of audible sound can reach over 200 dB peak. This can extinguish the flame on a single candle without affecting nearby lit candles. Most methods used to extinguish a flame using sound involve the nearfield and nonlinear airflow effects. Because time reversal focusing can occur far from the sources, the mechanism is different. Using high-speed video footage of the focal event, we can see the finer details of this millisecond scale focus interacting with the flame. Measuring the sound field during the focus event at and near the focal location also sheds light on the mechanism. So far, it has been seen that the focus pushes the flame outward, separating the plasma from its fuel source. The known formation of shock waves provides a possible explanation. Further research is being done to explore the cause of the extinguishing of the flame. This talk will show that not only is it possible to focus high amplitude sound waves but targeted flows of air as well.