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light sound waves

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

intergalactic stars

Researchers successfully recreate the sounds of stars through simulation softwares

It is well known that sound cannot propagate in vacuum as it requires a medium for its transmission. Sounds propagate as longitudinal waves in solids and fluids and also as a tranverse wave in solid structures. But scientists have been able to overcome this limitation as they have developed an innovative way for interpreting the signals which have been emitted by cosmos.

Researchers at University of Wisconsin-Madison have separated a different type of resonance which are caused by stars. These vibrations are actually variations in the temperature and the brightness of stars. Very powerful telescopes can spot these vibrations and then recreate the sounds of the stars with the help of computer simulations.

Jacqueline Goldstein, a graduate student in astronomy at University of Wisconsin-Madison said that a cello’s sound is because of its shape and size, similarly the vibrations of the stars are also dependent on their size and composition. Goldstein studies the connection between the structure of stars and their vibrations with the help of the software which simulates many stars and their frequencies. After comparing the simulations to the real stars, she can improve her model and make necessary changes.

For human beings to hear the sounds, the speed of the vibrations have to be increased by thousand to million times, besides repeating the frequencies from minutes to days. These are known as starquakes after their seismic variants on Earth and the field of study is called as astroseismology.

After the fusion of hydrogen in stars to heavier elements in the star cores, plasmic gas vibrates and hence the stars flicker. Researchers can know about the structure of stars through these fluctuations and also the changes which may occur in the star with the passage of time.

Goldstein studies those stars which are bigger than the sun as these are the ones which explode and lead to the formation of black holes, neutron stars and the heavy objects in the cosmos. Scientists want to study about the functioning of these stars and how they make an impact in the expansion and evolution of the universe.

With the help of professors of astronomy, Rich Townsend and Ellen Zweibel, Goldstein has created a computer software named GYRE which is plugged into the simulation software for stars, MESA. These softwares make it possible to develop models of different kinds of stars and observe their vibrations as they may appear to astronomers.

Since, GYRE and MESA are open source programs, they can be accessed freely by the scientists and modified. Goldstein is currently making a modified version of GYRE to take advantage of the data obtained by TESS.