Andrea Alù Explains How He Tricks Light and Sound
In a new "Scientific American" article, the renowned physicist describes his breakthroughs in designing metamaterials and cloaking objects.
Creating metamaterials that trick sound and light may sound more like science fiction than science, but that is what Distinguished Professor Andrea Alù (Physics), founding director of the Photonics Initiative at the Advanced Science Research Center at the CUNY Graduate Center (CUNY ASRC), does in his research. In a new article in Scientific American, the eminent physicist, a Blavatnik National Awards Laureate, describes in plain language his far-out inventions.
As Alù explains, metamaterials are materials that are engineered to “move beyond the traditional ways in which waves and matter interact, creating technologies where light and sound appear to disobey conventional rules.” He delves into the metamaterials that he and his colleagues have created, how these materials manipulate sound and light, and their many potential applications.
Alù is best known for his breakthroughs in manipulating waves. About 15 years ago, he worked with Nader Engheta at the University of Pennsylvania to design a metamaterial shell that can disguise an object by controlling light waves. Light waves that bounce off the shell cancel the light waves scattered by the object, making the object impossible to detect by external illumination. “From an electromagnetic point of view,” Alù writes, “it would appear not to exist.”
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Alù and his team subsequently produced a cloak that can significantly reduce the amount of radio waves that scatter from a cylinder, making it hard to detect by radar.
Metamaterial cloaks for small objects and longer wavelengths, such as those of sound, Alù explains, could change radar, wireless communications, and sensor technologies.
Alù has also created metamaterials that play with the polarization of light — the trajectory that light’s electromagnetic fields trace in space over time. Using thin layers of glass embedded with gold rods, he and researchers in his lab built a metamaterial that can rotate the polarization of light that travels through it.
In 2020, Alù’s research group at the CUNY ASRC created a metamaterial that allowed for the superconductivity of light. The invention offers an exciting platform for quantum technologies, Alù writes.
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He and his team have also played with time-reversal symmetry — the law that if a wave of light or sound can move from point A to point B, it can also move back from B to A with the same features. They have created a device that manipulates sound so that it travels only in one direction.
Similarly, the team has worked on objects that break Kirchoff’s law that reciprocal materials in equilibrium must absorb and emit thermal radiation at the same rate. The ultimate result, Alù writes, would be to enhance the amount of energy an object can harvest, which has implications for sustainability and smart building design.
“Metamaterials can be featured on the walls and windows of smart buildings to control and route electromagnetic waves at will,” Alù writes in the conclusion. “Nanostructured metasurfaces can shrink bulky optical setups into devices thinner than a human hair, enhancing imaging, sensing, and energy-harvesting technologies. Acoustic and mechanical metamaterials can route and control sound with an unprecedented degree of control.” With recent advances in fabricating nanoscale materials and scientists’ improved understanding of how light and matter interact, Alù expects many more wonders ahead.
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