The physics of knocking over LEGO minifigures with time reversal focused vibrations for use in a museum exhibit.

Time reversal (TR) is a method of focusing wave energy at a point in space. The optimization of a TR demonstration is described, which knocks over one selected LEGO minifigure among other minifigures by focusing the vibrations within an aluminum plate at the target minifigure. The aim is to achieve a high repeatability of the demonstration along with reduced costs to create a museum exhibit. By comparing the minifigure's motion to the plate's motion directly beneath its feet, it is determined that a major factor inhibiting the repeatability is that the smaller vibrations before the focal event cause the minifigure to bounce repeatedly and it ends up being in the air during the main vibrational focal event, which was intended to launch the minifigure. The deconvolution TR technique is determined to be optimal in providing the demonstration repeatability. The amplitude, frequency, and plate thickness are optimized in a laboratory setting. An eddy current sensor is then used to reduce the costs, and the impact on the repeatability is determined. A description is given of the implementation of the demonstration for a museum exhibit. This demonstration illustrates the power of the focusing acoustic waves, and the principles learned by optimizing this demonstration can be applied to other real-world applications.