Time reversal technique is used to knock over minifig targets. Credit: Brian Anderson.
A table covered in Lego minifigures. There is a whooshing sound, a pause, and then a single minifigure in the center of the table topples over, leaving the remaining minifigures standing.
Brian Anderson, a professor at the University of Utah, will present "Knocking over LEGO minifigures with time reversal focused vibrations: Understanding the physics and developing a museum demonstration" at the 181st Meeting of the Acoustical Society of America. The session will be held on December 2.
Anderson and his team use speaker shakers. They place Lego minifigures on the plate, choose a target, and measure the impulse response between the Lego minifigures and the target location. Sound waves that interfere at the target minifigure are created by playing that very response from the shakers. The Lego minifig is knocked over by the focused energy.
The demonstration was turned into a game for a museum exhibit in Switzerland. Two visitors are trying to knock over Lego minifigures on the other team.
Anderson said that the technique shows the power of focused vibrations.
Anderson said that time reversal can be used to focus sound in the body that is strong enough to destroy stones or tumors without surgery. I have used time reversal to locate defects in metal structures, such as storage canisters for spent nuclear fuel. Time reversal can be used to locate earthquakes or gun shots in an urban environment.
Lego down! The minifigures were knocked over by focused vibrations on December 2, 2021.
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