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Metadevices Could be Developed with 3D Printing and an Inverse Design Approach

23 January 2018

Technologies like wafer-thin eyeglasses, tiny, invisible smartphone cameras, disappearing materials that act like an invisibility cloak and more are one step closer to becoming a reality thanks to researchers at Northwestern University. The research team has used inverse design principles and a basic 3D printer to create highly efficient, non-resonant, broadband metadevices at millimeter-wave frequencies. This development could be revolutionary for consumer products, defense and telecommunications, like next-generation 5G wireless networks.

Inverse-designed metalenses. Simulated (A,B) and measured (C,D) spatial power distributions along the x-y plane at the output of the metalenses at 38 GHz. The input plane wave is generated by a horn antenna 1 m away on the left of the device while the output is measured with a probe antenna scanned along a 9 × 10 cm x-y plane for the first lens (A,C) and a 14 × 15 cm plane for the second lens (B,D). The first lens focuses perpendicularly polarized EM field 2λ away from the device whereas the second lens focuses it 15λ away. Schematics and pictures of the 3D-printed lenses are shown next to the simulated and experimental maps respectively. (E) and (F) Cross-section of the simulated (black line) and measured (red circles) power along the white dashed lines on the color maps for the first (E) and second (F) lens. Source: Northwestern UniversityInverse-designed metalenses. Simulated (A,B) and measured (C,D) spatial power distributions along the x-y plane at the output of the metalenses at 38 GHz. The input plane wave is generated by a horn antenna 1 m away on the left of the device while the output is measured with a probe antenna scanned along a 9 × 10 cm x-y plane for the first lens (A,C) and a 14 × 15 cm plane for the second lens (B,D). The first lens focuses perpendicularly polarized EM field 2λ away from the device whereas the second lens focuses it 15λ away. Schematics and pictures of the 3D-printed lenses are shown next to the simulated and experimental maps respectively. (E) and (F) Cross-section of the simulated (black line) and measured (red circles) power along the white dashed lines on the color maps for the first (E) and second (F) lens. Source: Northwestern University

"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 efforts in inverse-designed metadevices. "There's a lot that needs to be done in the research part, but we're going in the right direction."

This inverse design starts with a function and asks what structure is needed to achieve the desired result. Using computer modeling, optimization software and complex algorithms, the team set out to build metadevices that could bend or focus millimeter waves but avoided problems with conventional approaches like low efficiency, narrow bandwidth and the bulkiness of the devices.

"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.

Kumar compared this process to machine learning and said it could produce unexpected outcomes, like the functionality over a broad bandwidth.

Francois Callewaert, a graduate student from the McCormick School of Engineering who works with Aydin, developed the inverse design algorithm and performed the numerical simulations. Vesselin Velev, a physics and astronomy graduate student who works with Kumar, helped with the detailed millimeter-wave measurements.

Aydin described the impressive moment that the algorithm produced the design for a complex geometric shape.

"These were not known shapes, not intuitive shapes," Aydin said.

This presented its own problem: Conventional manufacturing methods would be difficult and expensive. The answer was in 3D printing.

"This is the heart of the study," Aydin said. "We're the first to combine these two to make working devices."

Kumar agreed. "The important thing to me is the multidisciplinary nature of it," he said. "We can design a lens in a way that it doesn't look like a lens."

A strength of the process was that it was imminently scalable from the microwave to the visible frequency range due to the flexibility of 3D printing.

"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."

The paper on this research was published in Scientific Reports.

To contact the author of this article, email Siobhan.Treacy@ieeeglobalspec.com


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