Whenever you hear the name Northwestern University, it’s a pretty good bet that something interesting is happening. Researchers at the university have been responsible for some fascinating breakthroughs involving 3D printing, from simulated extraterrestrial soil 3D prints to 3D printed tetrahertz lenses and more. Now a research team at Northwestern is working with metadevices, using inverse design principles and a 3D printer purchased from Amazon to fabricate highly efficient, non-resonant, broadband devices at millimeter frequencies. These metadevices could have a big impact on a number of areas like consumer products, defense, and telecommunications, including 5G wireless networks.
“I feel like we’re really on the verge of something big,” said Koray Aydin, Assistant Professor of Electrical Engineering and Computer Science at the McCormick School of Engineering, who is leading the research. “There’s a lot that needs to be done in the research part, but we’re going in the right direction.”
Inverse design starts with a desired function and asks what structure is needed to achieve that result. The team used computer modeling, optimization software and complex algorithms to build metadevices that could bend or focus millimeter waves but didn’t suffer from the same problems as those made by conventional approaches, such as low efficiency, bulkiness and narrow bandwidth.
“What we’ve achieved here is a new way of creating electromagnetic devices that achieve certain functions that conventionally seemed impossible to do,” said Prem Kumar, Professor of Electrical Engineering and Computer Science in McCormick and of Physics and Astronomy in the Weinberg College of Arts and Sciences.
Graduate student Francois Callewaert developed the inverse design algorithm and performed the numerical simulations, while Vesselin Velev, another graduate student, helped with the millimeter-wave measurements. Finally, the algorithm gave them the design for a complex shape.
“These were not known shapes, not intuitive shapes,” Aydin said. His thought then was, “How on Earth are we going to make this?”
3D printing, of course.
“This is the heart of the study,” Aydin said. “We’re the first to combine these two to make working devices.”
The metadevices, as described in a newly released paper entitled “Inverse-Designed Broadband All-Dielectric Electromagnetic Metadevices,” which you can access here, could include things such as wafer-thin eyeglasses, a microscopic smartphone camera, or aerodynamic sensors that can conform to the shape of an airplane wing. Other possibilities include actual invisibility cloaks – materials that can coat something to make it seem to disappear.
“The important thing to me is the multidisciplinary nature of it,” said Kumar. “We can design a lens in a way that it doesn’t look like a lens.”
According to Aydin, another benefit of the process is its scalability thanks to 3D printing’s flexibility; it can be utilized from the microwave to the visible frequency range.
“It is an exciting result,” said Alan V. Sahakian, the John A. Dever Chair and Professor of Electrical Engineering and Computer Science. “Where in the past somebody might have done a long analysis trying to approximate the behavior, here we essentially input the behavior we wanted into a computer and the computer optimizes a structure that has that behavior and then it comes out the other end of this three-dimensional printer. It is truly a breakthrough in the way you can solve problems in a seamless and convenient way.”
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