# Interdisciplinary sound-wave study holds promise for new technologies

Siv Schwink
8/17/2016

An array with a wave traveling through it before and after a modulation which changes the propagation pathway. Image courtesy of Taylor Hughes, University of Illinois at Urbana-Champaign.
Physics professor Taylor Hughes and mechanical science and engineering professor Gaurav Bahl of the University of Illinois at Urbana-Champaign are part of an interdisciplinary team that will study non-reversible sound wave propagation over the next four years, with a range of promising potential applications.

The National Science Foundation has announced a $2-million research award to the team, which includes University of Oregon physics professor Hailin Wang and Duke University electrical and computer engineering professor Steven Cummer. The grant is part of a broader$18-million NSF-funded initiative, the Emerging Frontiers in Research and Innovation (EFRI) program, supporting nine teams—a total of 37 researchers at 17 institutions—to pursue fundamental research in the area of new light and acoustic wave propagation, known as NewLAW.

An NSF news release issued August 16, 2016, emphasizes the great potential of this line of inquiry to transform the ways in which electronic, photonic, and acoustic devices are designed and employed, and to enable completely new functionalities.

"We're really excited about starting this project,” comments Hughes. “We looked at several possible funding opportunities and the NSF's Emerging Frontiers program ended up being the best fit for our ambitious, interdisciplinary focus.

“This is the first program I have worked on that is so tightly connected with engineering, and it is rewarding to know that our work might have a technological impact. We also have some nice plans for outreach efforts that go hand in hand with our research goals."

The specific research being done by the team from U. of I., Duke, and UO has implications for noise reduction, improvements in ultrasound imaging in healthcare, nondestructive sound-based testing of materials, and signal processing for communication systems.

Propagating waves—electromagnetic, light, or sound waves—are used in a very wide range of communication, computation, signal processing, and sensing systems. Devices used in these systems are made of naturally obtained materials which do not allow one-way propagation of waves (especially sound) while blocking the reverse path. The team will develop techniques to fundamentally control the directionality of sound wave propagation in newly engineered materials.

Unidirectional sound-wave propagation will enable building isolators and circulators for signal protection and routing, and for signal shielding and cloaking applications. Manipulating materials to allow waves only one direction of travel represents a significant engineering challenge that extends across physical domains from optics, to electronics, to acoustics.

The research team proposes a new concept for achieving non-reciprocal sound propagation, through spatio-temporal modulation of the material in conjunction with dispersion engineering of modes. The proposed research will experimentally develop the concept in three distinct multiphysical platforms spanning from nano-scale to macro-scale; including the coupling of phonons to electromagnetic and acoustic waves in structured electromechanical systems, and with defect states such as nitrogen vacancy centers in diamond. The team will ultimately demonstrate how 1D/2D engineered arrays of non-reciprocal unit cells can create novel, reconfigurable, unidirectional pathways for sound. The general nature of this approach potentially makes it directly extensible into optical and electromagnetic domains in the future.

This research project combines electrical engineering, physics, and mechanical engineering, offering students a unique interdisciplinary training opportunity. The effort will also help broaden participation of women and minority students in research, and will lead to development of innovative educational and scientific outreach activities, with significant involvement of undergraduate students.

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