Bahl research could impact ultrasound imaging, more

Assistant Professor Gaurav Bahl was awarded a 2017 Director of Research Early Career Grant from the Office of Naval Research. This competitive award of $1M over five years will allow him to pursue research on non-reciprocal systems for sound and microwaves.
Through his project, “Engineering nonreciprocal acoustic materials and microwave systems through phonon-assisted directional coupling,” Bahl will experimentally develop techniques for engineering new forms of wave propagation by means of engineered time-varying materials. He said he hopes to fill a fundamental scientific gap in the practical realization of non-reciprocal behavior that is unavailable in natural materials.  
Reciprocity is a property inherent to natural materials at steady state, which implies symmetry under time reversal. In other words, waves (e.g. sound, light, microwaves) propagating forward or backward through a medium exhibit identical propagation characteristics irrespective of direction. 
Bahl’s group had previously demonstrated opto-mechanical devices that exhibit very strong non-reciprocal characteristics and were inspired by concepts borrowed from atomic physics. The current project is in turn inspired by their success in opto-mechanical devices and aims to replicate an effect that is analogous to phonon-assisted directional scattering of light, for enabling non-reciprocal behavior in a new generation of systems.
Bahl said he hopes to exhibit fundamentally new mechanisms for reconfigurable non-reciprocity for sound waves and microwaves, through the design and experimental realization of spatiotemporally modulated coupling elements between waveguides and resonators. 
He said his results will lay the foundation for further miniaturization and development of deep sub-wavelength acoustic isolators, gyrators, and circulators. Potential impact, in both civilian and navy applications, includes manipulating acoustic and microwave signatures on demand, ultrasound imaging, cloaking, and shielding. 
Bahl leads a research group at Illinois that performs experimental research at the interface between optical and mechanical systems—in particular, the mechanisms by which light interacts mechanically with photonic microdevices. He joined the MechSE department in 2012.