LEGO Down! Focused Vibrations Knock Over Minifigures

Summary

In this engaging presentation at the 181st meeting of the Acoustical Society of America, Brian Anderson from Brigham Young University discusses the fascinating concept of time reversal in acoustics, where sound waves are focused to a specific point in space. Using LEGO minifigures as a visual demonstration, Anderson highlights how wave energy can be directed precisely, even knocking over LEGO figures. The technique has diverse applications, from medical treatments to submarine communication, and has drawn significant attention, especially at an interactive museum exhibit at ETH Zurich. The project has proven successful with 100% repeatability, engaging audiences while explaining complex scientific concepts in a fun and accessible way.

Takeaways

• 😀 Time reversal is a method of focusing wave energy to a specific point in space, such as sound waves.
• 😀 The demonstration uses LEGO minifigures to visually showcase the concept of time reversal, where focused sound waves make a LEGO figure jump into the air.
• 😀 Brian Anderson from Brigham Young University (BYU) explains that time reversal involves reversing the paths of sound waves to focus them on a target location.
• 😀 The original experiment was conducted at Los Alamos National Laboratory, and later developed further at BYU and ETH Zurich.
• 😀 The demonstration at ETH Zurich is part of a museum exhibit on wave propagation and time reversal, aimed at educating visitors about acoustics.
• 😀 The key challenge in the experiment was ensuring repeatability, as the LEGO figures sometimes bounced before the sound waves focused on them, causing missed demonstrations.
• 😀 A new approach was implemented using a laser to measure the vibrations of the LEGO minifigures, revealing that the bouncing interfered with the demonstration.
• 😀 The experiment was optimized using a cheaper eddy current sensor for the museum setup, allowing visitors to interact with the demonstration and choose where to focus the energy.
• 😀 Applications of time reversal technology include medical uses like destroying kidney stones non-invasively, as well as locating earthquakes and communicating between submarines.
• 😀 The demonstration drew attention from LEGO enthusiasts and children, turning the science experiment into a fun and interactive experience that encourages interest in acoustics and physics.

Q & A

What is time reversal in the context of this experiment?

Time reversal is a method used to focus wave energy to a specific point in space. In this experiment, it is applied to sound waves, where the waves are played in reverse to make them converge at a single point, creating a large energy focus that can physically move objects, like LEGO minifigures.

How does the LEGO minifigure demonstrate the concept of time reversal?

The LEGO minifigure is placed on a vibrating plate. When sound waves are focused beneath it, the minifigure is knocked into the air. This occurs because the waves converge at a point directly under the figure, providing enough energy to move it.

What challenge did the researchers face with the LEGO demonstration?

The main challenge was the repeatability of the demonstration. While the waves generated enough energy to move the LEGO figure, it only worked about a third of the time due to issues with the minifigure bouncing before the waves converged.

How did the researchers address the bouncing problem with the LEGO figure?

The researchers adjusted the amplitude of the waves. They reduced the amplitude enough to prevent the LEGO from bouncing before the waves focused, but kept it high enough to launch the LEGO into the air when the focus occurred.

What was the role of the laser sensor in the original experiment?

The laser sensor was used to measure the vibrations on the plate and track the position where the waves were focused. However, it was an expensive piece of equipment, leading the team to seek a more cost-effective solution for practical demonstrations.

What alternative sensor was developed for the museum demonstration?

The researchers developed an eddy current sensor, which is cheaper and can detect vibrations in metal plates. This sensor was used to interact with museum visitors, allowing them to select a LEGO minifigure to knock over by focusing the energy at its location.

How did the team ensure the demonstration was engaging for museum visitors?

The team allowed museum visitors to actively engage with the demonstration by selecting which LEGO minifigure to knock over. The setup was designed to be a game of chance, where the repeatability of the demonstration was intentionally reduced to make it more interactive and fun.

What are some potential applications of time reversal technology mentioned in the presentation?

Potential applications of time reversal include non-invasive medical treatments like breaking kidney stones, detecting structural damage, locating earthquakes, and even communicating between submarines using focused wave energy.

How does time reversal relate to medical treatments like kidney stone removal?

In medical treatments, time reversal can focus enough energy to target kidney stones non-invasively. The waves are focused on the stone, causing it to heat up and eventually disintegrate, removing the need for surgery.

Could time reversal technology be used for large-scale applications, such as in military settings?

While the technology is capable of focusing wave energy to specific points, it is unlikely to be scaled up for destructive military purposes. However, its potential for medical uses like treating brain tumors and kidney stones remains an exciting prospect.