Getting Antennas Into Shape

Many of today’s biggest communications networks are largely invisible, as the wires and switches of the past have been replaced with wireless radio frequency (RF) transmissions. Between multiple cell phone standards, satellite internet, Wi-Fi, RADAR, and hundreds of other applications, each using its own frequency bands, the airspace is starting to get crowded. Any connected device that wants to communicate on any of these frequencies needs an antenna — or more accurately, an antenna for each frequency band it needs to communicate on.

The shape of an antenna directly influences its operating parameters, such as frequency range and beamwidth, so there is no one-size-fits-all option. As such, if a device needs to communicate via several methods, the number of antennas it must carry necessarily grows, which can quickly become impractical — especially for mobile applications.

Some of that extra bulk may soon be unnecessary for the chattiest of devices, thanks to a new development that just came out of the Johns Hopkins Applied Physics Laboratory. Rather than building a separate antenna for each use case, this research group says that one antenna will do just fine, thank you — as long as it can do a little bit of controlled shape-shifting. By dynamically changing its geometry, the shape-shifting antenna can perform the roles of multiple traditional antennas, offering greater versatility and efficiency in applications ranging from military communications to space exploration.

These antennas leverage the unique properties of a material called nitinol — an alloy of nickel and titanium — which can transition between two remembered shapes when heated or cooled. The team pioneered a method to 3D-print nitinol with two-way shape memory, allowing the antenna to alternate between a flat spiral disk (when cool) and a cone spiral (when heated). This transformation enhances its ability to adapt to different operational requirements. Heating the structure without compromising its RF properties was particularly complex, necessitating the invention of a new power line design capable of handling high currents.

The nitinol’s inherent properties made 3D printing difficult, as the antenna attempted to change shape during the fabrication process. Extensive experimentation and refinement of manufacturing parameters were required to achieve consistency and scalability. Despite these hurdles, the team successfully optimized the process, enabling broader applicability and laying the groundwork for future advancements.

This technology has transformative potential for a variety of fields, offering a lightweight and adaptable solution for communication systems, mobile networks, and even space missions. Looking ahead, the researchers are going to explore the possibility of controlling the shape-shifting action such that in-between states can be stably achieved, rather than just the present bistable design. In any case, the shape-shifting antenna's ability to provide operational agility with a minimal physical footprint marks a significant leap in antenna design and functionality.