Bahl, Stephani reflect on PECASE awards
No other university in the nation had more than one PECASE winner among mechanical engineering faculty in 2019.
The National Science and Technology Council (NSTC) established the PECASE in 1996 to recognize outstanding scientists and engineers early in their research careers. The award’s winners receive a citation, a plaque, and five years of funding to help advance their research.
A number of U.S. research institutions work with the PECASE to nominate candidates. Stephani was nominated by NASA and Bahl by the Department of Defense.
Stephani’s connection with NASA began in her graduate studies and has continued to grow since. She attributes much of this award to the relationship she has developed with researchers at NASA and the work they have collaborated on.
Stephani’s work develops simulations of the heat loads that occur on NASA vehicles entering the Earth’s atmosphere at hypersonic speeds. The process involves a period of intense loading that could determine the success or failure of the vehicle within the mission. The process lasts minutes, but there are chemical reactions and physical processes occurring over a broad range of length and time scales throughout reentry.
Stephani must determine what scales to consider, determine what matters to the big picture, and design her models around that. The work aims to identify what material, what material configuration, and what material thickness can successfully withstand reentry for each vehicle.
Stephani’s work applies to U.S. Air Force vehicles as well and, although they share a like philosophy, they pose extremely different challenges. Air force hypersonic vehicles undergo a similar variety of loading situations throughout their missions, but mission requirements dictate an entirely different set of capabilities and performance metrics. The difference in geometry of the typical NASA vehicle and the typical air force vehicle also introduces many unique considerations. Despite these differences, her lab develops the tools for both organizations and a variety of missions.
“No PECASE is won by a single person," she said. "You can think of it sort of like a web—one person can only achieve so much, but if you can find new ways to connect and new ways to bring other researchers together through your work, that’s really at the heart of what the PECASE is. If you cultivate those connections, the impact of your research is going to be so much greater.”
Bahl’s research lives in the intersection between mechanical engineering, optical engineering, and electrical engineering. His projects span from micro-electro-mechanical-systems that are nanometers in size, to optical fibers that are meters long.
Bahl allows a series of questions to fuel his investigations, especially on systems that can operate even in the presence of defects or damage. On the subject of communication systems, Bahl asks, “Can we make a waveguide that is so resilient that wave propagation is unaffected, even if there is a defect within the waveguide material?”
Beginning in 2012, Bahl began to study Brillouin Scattering, which is a fundamental interaction between sound waves and light. The experimental devices for this series of works borrowed from principles behind whispering galleries, which were first understood by Rayleigh in St. Paul’s Cathedral in London. Both St. Paul’s Cathedral and Bahl’s experimental devices allow sound to travel around the structure and resonate, but Bahl’s devices also perform this feat for light waves. For the cathedral, this means sounds as faint as whispers can be clearly heard across the building. For Bahl, it means the miniscule interactions between light and sound can be measured experimentally.
Bahl came from an electrical engineering background, working with micro-electro-mechanical systems during his PhD. He shifted to focus on optics, fiber optics, and opto-mechanics during his post doctorate study.
Similarly, he wants the students in his group to explore different disciplines to gain a versatility that will make them better engineers. “It doesn’t matter which department you’re in, if you’re an engineer and you’re excited about the topics, just go do it.”