EFRI NewLAW: Reconfigurable pathways and directionality for sound using time-varying engineered materials

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Propagating waves (electromagnetic, light, sound) are the fundamental phenomena that are used in a very wide range of communication, computation, signal processing, and sensing systems. However, naturally obtained materials fundamentally do not allow one-way propagation of waves (especially sound) while blocking the reverse path. This award supports fundamental research for developing techniques to control the directionality of sound wave propagation in engineered materials. Results from this project will have large social impact in multiple areas -- engineering the directionality of sound waves can enable better environmental noise reduction, improvements in ultrasound imaging in healthcare, nondestructive sound-based testing of materials, and even signal processing for communication systems. 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.Reciprocity is a fundamental characteristic of sound propagation in stationary media, wherein time-reversed outputs map exactly back to the input. However, non-reciprocal behavior is required for building isolators and circulators for signal protection and routing, and for signal shielding and cloaking applications. Manipulating materials to exhibit non-reciprocity is thus 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.