The shape of an antenna largely determines its operational capabilities, which are traditionally fixed during manufacturing. A shape-shifting antenna, however, can dynamically adapt to different radio-frequency (RF) bands, effectively replacing multiple static antennas. This innovation offers improved spectrum flexibility, enhanced adaptability, and the ability to switch between short- and long-range communications.

From Sci-Fi Inspiration to Cutting-Edge Reality
Jennifer Hollenbeck, an electrical engineer at APL, drew inspiration from The Expanse series, which depicts futuristic, shape-changing technology. "I have spent my career working with antennas and wrestling with the constraints imposed by their fixed shape," said Hollenbeck. Recognizing the lab's expertise, she initiated collaboration in 2019 with Steven Storck, then leading additive manufacturing research at APL.

Shape memory alloys like nitinol, a nickel-titanium compound, were central to the project. These materials can change shape at varying temperatures and return to their original form when heated. Although nitinol is commonly used in medical and aerospace applications, its complexity made it challenging to manufacture for new purposes. Mechanical engineer Andy Lennon and his team tackled this by developing methods to 3D-print nitinol components, paving the way for novel applications, including this antenna.

Overcoming Design Challenges
The team's initial attempts to build a functional antenna met hurdles, particularly in achieving the desired flexibility and RF performance. "It turned out to be a really complicated design, and it didn't work as well as I would have liked," admitted Hollenbeck. Undeterred, the team secured a Propulsion Grant to refine their approach.

They designed an antenna that morphs from a flat spiral disk to a cone spiral when heated. However, heating the antenna without compromising its RF properties required an innovative power line design, developed under the leadership of RF engineer Michael Sherburne.

Sherburne explained, "For peak heating, the power line has to handle a lot of current. We had to go back to fundamentals to make this work."

Perfecting the Process
Another challenge was 3D-printing nitinol consistently. "There's no recipe for processing this material," said additive manufacturing engineer Samuel Gonzalez. Printing required weeks of experimentation and overcoming obstacles like material deformation during the process. "We made shrapnel in the printer a few times because the antenna is trying to change shape as you're printing it," added Mary Daffron, a colleague on the project.

Despite the hurdles, the team optimized their methods, reducing processing times and expanding the technology's scalability. Future goals include adapting the manufacturing techniques to other machines and exploring materials that respond to different temperature ranges.

Applications and Future Potential
The shape-adaptive antenna could transform applications ranging from mobile networks to space exploration. APL Chief Engineer Conrad Grant noted, "The shape-shifting antenna capability demonstrated by this team will be a game-changing enabler for many applications and missions requiring RF adaptability in a low-size and -weight configuration."

APL is actively pursuing patents for this technology, including the antenna, the power line design, and methods for phased array antenna creation.

Research Report:Two-Way Additively Manufactured Shape Memory Alloy Wideband Reconfigurable Compound Antenna

Related Links
Johns Hopkins University Applied Physics Laboratory
Space Technology News - Applications and Research