Researchers demonstrate storage and release of mechanical waves without loss of energy

In several technologies which are used today, light and sound waves are the fundamentals for transporting energy and signals. However, until now there has been no method to store a wave for a long period of time and then redirect it to a specific location when needed. This would provide the opportunity to manipulate waves for several purposes such as quantum computing, storing information, energy harvesting and many more.
A team of scientists led by Andrea Alù, founding director of Photonics Initiative, Advanced Science Research Center, CUNY and Massimo Ruzzene, Aeronautics Engineering professor at Georgia Tech has demonstrated experimentally that it is possible to capture a wave and store it efficiently while redirecting it later to a specific location. The work appears in Science Advances journal.
Alù said that the experiment demonstrates new opportunities can be unlocked in wave scattering and propagation through unconventional scattering methods. Researchers found ways to change the basic interaction between waves and particles. On striking an obstacle, a light or sound wave can go through two processes, partial absorption or reflection and scattering. In absorption, the wave is immediately converted to different forms of energy including heat. For those who cannot absorb waves, they are reflected and scattered.
In this experiment, the aim of the researchers was to find some technique to mimic the process of absorption in which the wave would not be converted to any other form instead stored in the material. This is known as coherent virtual absorption and it was introduced by ASRC two years ago.

For proving the theory, it was necessary to tailor the time evolution of waves so that on contacting non-absorbing materials, they would not be scattered, transmitted or reflected. This would prevent the wave from escaping and store it inside the material efficiently. Then it could be released on demand. In the course of the experiment, two mechanical waves were propagated in opposite directions along a carbon steel waveguide that had a cavity. Time variations of every wave were controlled so that the cavity would retain all the energy. The excitation of one of the waves was stopped which enabled the researchers to control the stored energy and send it towards a specific direction.
The experiment was performed using elastic waves which traveled inside a solid material. It can also be replicated for light and radiowaves thus opening the doors to exciting opportunities such as efficient harvesting of energy, wireless power transfer and greater control on wave propagation.
Research Paper: Coherent virtual absorption of elastodynamic waves

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