IMSE Seminar with James Friend on Fast Acoustofluidics and Acoustic Streaming

When Chladni demonstrated the eponymous patterns in sand that formed across vibrating membranes to an audience at the Tuileries Palace in 1809, he found abundant financial support from Napoleon Bonaparte and the genesis of a bitter relationship with Félix Savart. The former amply funded his travels, while the latter argued that fluid flow adjacent the membranes helped drive the particles' motion. This phenomenon—acoustic streaming—mysteriously appears across history, influencing Michael Faraday in his experiments in 1831, attracted the curiosity of Lord Rayleigh in 1884, and puzzled researchers in the 1950's, wondering why there was a wind generated from quartz crystals. Little did they know that this phenomenon would grow to become valuable in its own right to drive fluid flows in micro to nano-scale devices, and command the recasting of analyses first started by Rayleigh and continued over the years to the present day.

Acoustic streaming is a nonlinear second-order phenomenon that generally produces rapid (~10 cm/s) fluid flow but only against weak (~10 kPa) pressure gradients. Traditional analysis presumes that the flow is so weak that it is essentially negligible in comparison to the acoustic wave responsible for it. In modern acoustofluidics, this has never been true. We illustrate this fact through a new approach to the problem that is mathematically challenging but produces a fruitful outcome. We also describe a new form of acoustic streaming—acoustogeometric streaming—that is still nonlinear but relies on the interaction between the acoustic wave and the bounds of the fluid passage to produce not only rapid flows, but flows that produce very large pressures in excess of 1 MPa. Specifically, we demonstrate the ability to propel fluids at 6 mm/s in 20-150 µm wide, 100 nm tall nanoslit geometries and to transport, split, combine, and mix ~100 femtoliter droplets of fluid, and broaden our presentation to show the many ways acoustic streaming is and could be useful.

James Friend leads the Medically Advanced Devices Laboratory in the Center for Medical Devices at the University of California, San Diego. He holds the Stanford S. and Beverly P. Penner Endowed Chair in Engineering and is a professor in both the Department of Mechanical and Aerospace Engineering, Jacobs School of Engineering and the Department of Surgery, School of Medicine. He spent 14 years abroad as a faculty member in Japan and Australia before returning to the US. His research interests are principally in exploring and exploiting acoustic phenomena at small scales, mainly for biomedical applications. He currently supervises a team of 7 PhD students and one post-doctoral staff member. Over the years, he has published over 280 peer-reviewed research publications (H-factor = 54) and has 25 granted patents, completed 35 postgraduate students and supervised 23 postdoctoral staff, and been awarded over $29 million in competitive grant-based research funding. He most recently co-founded GlideNeuro, an endovascular intervention technology company, and Sonocharge, a rapidly rechargeable battery company that employs acoustic streaming and which has grown to a valuation of $22M. Among other awards, he received UCSD's Distinguished Teaching Award in 2021, was noted as a highly cited author of the Royal Society of Chemistry in 2020, is a Fellow of the IEEE from 2018, a Fellow of the Royal Society of Chemistry from 2022, and was awarded the IEEE Carl Hellmuth Hertz Ultrasonics Award from the IEEE in 2015.

Faculty, students, and the general public are invited.