The researcher behind the process, called targeted sound vibrations (or time reversal), is Professor Brian Anderson. The process involves focusing vibrations at a target location that may be far from where the vibrations originated. The term ‘time reversal’ is not about time travel; rather it means the reversal of sound waves.
To explain the process, Professor Anderson explains: “Time reversal is really like ventriloquism. But instead of throwing our voice to another place, we’re focusing vibrations at a target location that may be far from where the vibrations originated.”
To achieve this, the researchers activate an impulse from a sound source and record the response using a sensor at the targeted location. The sensor is able to catch the entire sound (including reflections and echoes from the environment) as the waves bounce around the environment before they reach the sensor. By using custom software, the researchers were then able to reverse the signal. This leads to the sound waves retracing their steps, although this time the researchers can direct the sound waves to a target location.
To demonstrate the technique, the researchers amusingly targeted sound at a series of LEGO figures. They showed how LEGO blocks and figures leap in the air before they crash to the ground. The scientists also demonstrated the process using grains of salt sprinkled onto a table. When the sound is concentrated, hundreds of grains are seen to rise and fall, appearing like a fountain of water rather than crystals of sodium chloride.
This is demonstrated in the video below:
On a more serious level, the researchers have used the sound waves to locate cracks in nuclear waste storage containers. Other researchers are testing out the process to track for objects deep under water (based on the process being superior to convention sonar). Another application includes the destruction of kidney stones in patients, without invasive surgery.
The technology is described in the publication The Journal of the Acoustical Society of America. The research paper is headed “Time reversal focusing of elastic waves in plates for an educational demonstration.”
