Researchers from the Photonics Initiative at the Advanced Science Research Center at The Graduate Center, CUNY (CUNY ASRC), and Georgia Tech have made a breakthrough by demonstrating the topological order based on time modulations for the first time.
The paper published in the journal Science Advances is authored by Andrea Alù, founding director of the CUNY ASRC Photonics Initiative and Professor of Physics at The Graduate Center, CUNY, and postdoctoral research associate Xiang Ni, together with Amir Ardabi and Michael Leamy from Georgia Tech.
In topological insulators, electrical current flows only on the material’s surface, not in the interior. Recent progress in metamaterials has extended these features to control the propagation of sound and light following similar principles.
Previous work conducted by Physics Professor Alexander Khanikaev from the labs of Alù and City College of New York used geometrical asymmetries to create topological order in 3D-printed acoustic metamaterials. The sound waves were confined to travel along the object’s edges and sharp corners. However, they weren’t fully constrained, and they could travel either forward or backward, limiting the overall robustness of this approach to topological order for sound. Certain types of imperfections in these materials reflect the sound waves propagating along the boundaries.
The new experiment addresses this issue, showing topological order can also be induced by time-reversal symmetry breaking. The researchers designed a device made of an array of circular piezoelectric resonators arranged in a honeycomb lattice bonded to a thin disk of polylactic acid. This device is then connected to an external circuit that provides a time-modulated signal that breaks time-reversal symmetry. The sound propagation becomes truly unidirectional and strongly robust to disorder and imperfections.
This new design allows programmability; the waves can be guided along a variety of different reconfigurable paths with minimal loss. Systems that use acoustic wave technology like Ultrasound imaging, sonar, and other electronic systems can benefit from this solution.
The new finding will also pave the way for cheaper, lighter devices that use less battery power and function in harsh or hazardous environments.
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