By: Dr. Steven Storck, Ms. Mary Daffron, Ms. Jennifer Hollenbeck, Dr. Michael Sherburne, Mr. Howard Feldmesser, and Mr. Andrew Lennon
Image Above: Two-way shape memory alloy antenna in the actuated configuration. Photo credit: Ed Whitman at JHU/APL. Taken at JHU/APL in January 2025.
A novel two-way shape memory alloy technology, developed by a team at JHU/APL, has led to an incredibly impactful application and has helped to redefine how antennas systems are designed. The ability to manufacture advanced technologies using new 3D printing methods allows one to think through how to best integrate a variety of components into systems which makes maintenance easier.
Imagine a future where a worn-out antenna element from a phased array antenna platform comes out of a satellite orbiting the moon. This communication satellite is providing a critical link between astronauts on the moon exploring the surface and provides time-critical mission control communications back to Earth. If anything happens to the astronaut’s lunar vehicle, timely launch of supplies to keep the astronauts alive as they wait for a recovery vehicle becomes a matter of life or death. Within an hour, another satellite takes the worn-out element using its robotic arm and replaces it with a new antenna element launched from Earth a few weeks earlier. This in-space maintenance operation saves millions of dollars by avoiding the need to launch an entirely new communication satellite. Meanwhile, researchers back on Earth are in the process of figuring out how to do the same advanced manufacturing of the antenna and other critical parts on the moon, cutting weeks of time out of resupply and maintenance missions. This scenario is no longer science fiction, but an attainable reality in the near future with the insertion of key future technology. Thanks to the expertise of scientists and engineers at Johns Hopkins University Applied Physics Laboratory (JHU/APL), a new paradigm in logistics is coming in communications.
Over the past decade, researchers at JHU/APL have learned to harness Shape Memory Alloys (SMA), particularly nitinol, using additive manufacturing. This material is made up of nickel and titanium and had its early roots at the Naval Ordnance Laboratory (NOL) in 1959. This material in its superelastic form has found its way into flexible glasses and orthodontic braces due to its superior elastic properties. However, beyond its elastic properties, nitinol in its shape memory compositions is able to recover from deformation and go back to its original shape when heated. This seemingly magical material exploits a solid-state phase transformation that appears to “remember” a high temperature shape. In the high temperature phase, all of the atomic bonds between metal atoms are at right angles (i.e., square) to one another, but in the low temperature phase all of those angles shift by a small amount, and the direction in which they shift is somewhat random. Mechanically deforming the nitinol at low temperature results in “detwinning” the atomic structure. Detwinning will take the random bond angles and align them in a common direction, resulting in large-scale shape change. When the temperature of the metal is raised above the phase transformation temperature, the atoms want to return to the configuration where all of the bond angles are square again. The shortest path that each atom can take to get back to that high temperature phase is to go back to where they originally started – the “remembered” high temperature shape!
The temperature range where the nitinol changes shape can be tuned with both composition (e.g., the ratio of nickel to titanium, or addition of ternary alloying elements) and the manufacturing process.[1],[2],[3] In industry, this material typically exists as wires and sheets, limiting its true potential. Chief Scientist Steven Storck and his team, including mechanical engineer and materials scientist Andrew Lennon, figured out how to print nitinol in a powdered form using the laser powder bed fusion (LPBF) method. In this process, solid material is formed by strategically melting metal powder in a layer-by-layer approach. This enables fabrication of complex shapes and materials that cannot be manufactured any other ways, such as topology optimized or latticed structures. While nitinol is very challenging to work with in both traditional and advanced manufacturing processes, manufacturing experts at JHU/APL developed methods to additive manufacture nitinol structures that can actuate via temperature change in not just one direction, but in two directions, resulting to two “remembered shapes.” Leveraging these novel manufacturing methods and nitinol’s SMA properties, several functional demonstrators have been developed that exhibit two-way shape memory behavior.
In 2021 a JHU/APL antenna engineer, Jennifer Hollenbeck, proposed an idea for an internal program that funds novel research. Being a true connoisseur of science fiction novels, Hollenbeck took inspiration from The Expanse sci-fi series written by James S. A. Corey where an alien material called the “protomolecule” can make shape-changing structures. According to Jennifer, “I have spent my career working with antennas and wrestling with the constraints imposed by their fixed shape. I knew APL had the expertise to create something different.” Due to JHU/APL’s unique capability for cross-department collaboration, she reached out to the additive manufacturing team and began a new research effort aimed at applying the novel use of additively manufacturing SMAs to antennas. An initial prototype was made using a horn antenna design and a one-way SMA. Shortly after that, the team started pursuing a double spiral antenna using the newly developed two-way SMA additive manufacturing process. This resulted in the creation of a reconfigurable antenna that can change both its frequency bands and antenna patterns to a large degree. After an exhausting two years, the team of researchers struck success and published their novel findings of the two-way SMA antenna in the journal American Chemical Society Applied Engineering Materials. [4] Their paper was selected as the journal’s cover page in an upcoming issue, highlighting its potential for impact.
Figure 1. Left: Two-way shape memory alloy antenna in the retracted configuration. Right: same antenna in the actuated configuration. Photo credits: Ed Whitman at JHU/APL. Taken at JHU/APL in January 2025.
In order to make an antenna out of the new two-way SMA technology, the manufacturing process and performance must be both repeatable and reliable. To make matters more challenging, the modified nitinol, with its higher concentration of nickel, created significant manufacturing challenges. Additive manufacturing engineer Samuel Gonzalez explained, “We have a lot of experience optimizing processing parameters and designs for alloys, but this was a step beyond. There aren’t many people out there, if anyone, printing this material, so there’s no recipe for how to process it.” Usually, it takes the team less than four days to process a conventional alloy, but this particular material took two to four weeks of build time to dial in the settings. Materials and process engineer Mary Daffron said of the high level of difficulty involved in printing with such a material: “We made shrapnel in the printer a few times because the antenna is trying to change shape as you are printing it, due to the heat inherent to the manufacturing process. It wants to peel apart.” However, this manufacturing challenge was overcome with novel processing techniques and the process is able to achieve the performance necessary to create the two-way SMA antennas.
The next step was determining a reliable way to change the actuation state of such a complex antenna. The team, with electrical engineer, Howard Feldmesser, and mechanical engineer, Kyle Lowery, leading the way, leveraged lessons learned about electrical actuation of 3D printed nitinol from a previous JHU/APL project on space deployable structures. The nitinol heating method used in this prototype is called resistive heating, which is where direct current is passed through a conductive material and heat dissipated by the material’s electrical resistance increases the temperature. The temperature of the nitinol, and by extension the state of transformation from the low to high temperature phase, can be estimated by measuring the electrical resistance of the nitinol as current flows through it. The ability to indirectly sense physical movement in the transmission line, by measuring its electrical resistance while the antenna is heating up is an incredible advantage as it obviates the need for other sensors that would negatively impact the antenna’s performance and would increase the mechanical and electrical complexity. Electrical engineer, Michael Sherburne, worked to develop an entirely new transmission line to prevent negative interactions between the RF signal to/from the antenna and the heating current. Once these challenges were solved, Howard Feldmesser was able to develop a control system that measures when the antenna is fully actuated and fully retracted.
This ability to both efficiently and compactly control the antenna’s actuation is important because overheating the antenna could negatively affect its lifetime, and would more quickly deplete the batteries of a system. Especially for unmanned and space assets, battery power is at a premium. The antenna’s actuation state can be changed (for this particular size) in under ten seconds or faster if more power was used. Once the state has been changed, it can reduce the heating or cooling rates to conserve power. Another interesting aspect about the thermal SMA technology is that it can take advantage of the ambient temperature environment to keep the antenna in one actuation state and only use power to have it change shape into another, reducing complexity of thermal systems. There are some applications where the antenna only needs to change shape when ambient thermal environments change, completely eliminating the need for any thermal systems at all, a major reduction in both power and space requirements. In addition, the antenna could be a part of the surface of a structure and then deploy from the surface, further reducing the Size, Weight, and Power (SWaP) of an overall system.
One of the complexities in creating such advanced antenna technology is the integration of multiple systems. During the engineering process, the team initially tried to have a thermal heating wire directly on top of the double spiral antenna. This turned out to become a complex engineering challenge to make the wire reliably conform to the surface of the antenna as any deviations from touching the surface degraded the antenna’s signal. However, the additive manufacturing team was able to quickly come up with a solution where a groove is directly manufactured into the antenna to lay the wire in. This rapid iteration in the design method does not increase the complexity of the manufacturing process but dramatically decreased the challenge in running the heating wire and improved the overall performance of the system by allowing the heating wire to be embedded in the antenna.
Figure 2. Left: earlier spiral antenna prototype with heating wire element on top of the spiral antenna. Right: newest spiral antenna prototype with heating element wire inside the spiral antenna. Photo credits: authors of the article. Taken at JHU/APL in 2024.
The ability to quickly solve engineering challenges enabled by the agility of additive manufacturing is important for faster acquisition of new technologies, especially when needing to make specialized components.
During this entire effort, digital engineering was at the forefront driving the entire development process. Hollenbeck, Kyle Sibert (electrical engineer), and Sherburne used Computational Electromagnetics (CEM) to model the antenna’s expected performance. The antenna itself is of such complexity that it falls under a class known as non-conformal antennas. This means that there is no closed form mathematical solution. Instead, CEM software had to be used. In addition, thermal modeling was done by thermal engineer Daniel Eby and Howard Feldmesser to determine what type of thermal approach would be best for an antenna being used at aircraft relevant altitudes. All of this modeling saved the team countless hours and funding during the prototyping stage as iterations can all be done digitally. However, like any model, it needs to be validated before one can use it to further fine tune its performance. This is where the team went to JHU/APL’s Space Exploration Sector to make use of their antenna range. Katherine Wolff was the RF engineer who calibrated the range and took the measurements. Decoupling the RF signal line from the DC power line to prevent equipment issues when measuring the antenna was another challenge to overcome. Typically, RF engineers do not work with both DC and RF signals on the same line. The test results agreed well with the CEM and thermal modeling, allowing the team to make new types of antenna designs with more confidence in the modeling approach.
Why is a reconfigurable antenna of such importance to the Department of Defense and society as a whole? The promise lies in the ability to take multiple antenna systems and use just one. Imagine being able to take a complex set of antennas to go across multiple communication bands and instead replace them all with just one antenna system. This can significantly decrease the size and weight of such platform. This becomes especially important in all domains of ground, sea, air, and space where power and size constraints become of great concern. To set an envisioned use case between the various domains using this antenna technology, we can start in the space domain. A reconfigurable antenna that allows for multiple communication bands could be used for satellite-to-satellite and satellite-to-ground terminals or satellite-to-aircraft for space applications:
Figure 3. Concept illustration of shape shifting two-way shape memory alloy antenna technology for cislunar applications. Credit to JHU/APL illustrator Stephen H. Hansen.
When going in between domains from space to air, the communication from satellite-to-aircraft could then be relayed from reconfigurable antenna technology within the aircraft itself. The aircraft can then relay this communication with other aircraft, ships, or to warfighters on the ground as shown in the figure below.
Figure 4. Concept illustration of shape shifting two-way shape memory alloy antenna technology for air applications. Multiple colors for both top and bottom antenna configurations represent multiple frequency bands that can be used in each configuration. The shared yellow color corresponds to the shared frequency band (same antenna performance) between configurations. Credit to JHU/APL illustrator Stephen H. Hansen.
Communication from the aircraft to a ship using a reconfigurable antenna technology can then be relayed from vessel-to-vessel and a variety of other assets in the joint force using a single antenna system:
Figure 5. Concept illustration of shape shifting two-way shape memory alloy antenna technology for Naval applications. Credit to JHU/APL illustrator Stephen H. Hansen.
Finally, from any of the already mentioned domains (sea, air, and space), the warfighter on the ground can communicate to any of these military assets without being bogged down carrying multiple antennas to communicate to all of them. The future reconfigurable antenna could be integrated within one’s armor.
Figure 6. Concept illustration of shape shifting two-way shape memory alloy antenna technology for ground applications. Credit to JHU/APL illustrator Stephen H. Hansen.
In addition, shape shifting antennas using nitinol can be used as the outer covering of devices such as mobile phones where there is a lack of room to incorporate larger antennas for more gain. The structural strength of nitinol also makes them useful as potential outer enclosures for systems. This potential ability to integrate antennas into the surfaces of structures and platforms can make such configurations easier to pack, carry, and ship. This concept is highlighted in the illustration below:
Figure 7. Concept illustration of a shape shifting antenna as a part of the enclosure of a mobile phone. This can allow for higher gain antennas that does not take additional space within a platform (other than the internal electronics needed to route signals to and from the antenna). This concept could be taken to a wide variety of applications and this illustration is just an example use case. Credit to JHU/APL illustrator Stephen H. Hansen.
The ability to seamlessly communicate between multiple platforms in a small and compact size that can be (most importantly) maintained at the edge is the vision the team has for the military. The ability to change communication frequencies and antenna patterns reliably will help keep this technology relevant for applications far into the future.
It is critical to note that such a novel capability would not be possible without the use of advanced additive manufacturing techniques. Using these advanced techniques also means that we have the ability to scale production for complex shapes. Use of additive manufacturing and digital engineering also means that parts can be designed and engineered by experts and the manufactured by equipment at the point of need. The potential of distributed advanced manufacturing was recently demonstrated by a Navy ship which was able to replace critical components with an on-board hybrid metal manufacturing machine. Instead of months to qualify a vendor, manufacture, and then ship the replacement part, the Navy was able to reverse engineer, produce, and install the part within five days. Advanced manufacturing is certainly a key ingredient in the future of logistics. The ability to use additive manufacturing means that a systems-level approach can also be applied to antenna architecture design and allows for rapid manufacturing and maintenance of reconfigurable antenna components.
The future of communications and logistics is making waves with the advent of advanced additive manufacturing capabilities. The warfighter of the future will have better, faster sensing and communication capabilities and the ability to adjust on-the-fly to tactical and practical concerns.
The views expressed in this article are those of the author and do not necessarily reflect the official policy or position of the Air Force, the Department of Defense, or the US Government.
About the authors
Steven Storck (Steven.Storck@jhuapl.edu) is a chief scientist focusing on manufacturing and materials development at JHU/APL. He is an expert in additive manufacturing of complex materials including nitinol-based materials. Mary Daffron (Mary.Daffron@jhuapl.edu) is a materials and processing engineer working on complex manufacturing challenges including additive manufacturing of nitinol. Jennifer Hollenbeck (Jennifer.Hollenbeck@jhuapl.edu) is a leading expert in antennas. Howard Feldmesser is an electrical engineer with a long history of groundbreaking work in analog circuits and power supplies (Howard.Feldmesser@jhuapl.edu). Andrew Lennon is a mechanical engineer and materials scientist with expertise in characterization and microstructure tailoring of complex materials, including nitinol shape memory alloys (Andrew.Lennon@jhuapl.edu). Michael Sherburne (Michael.Sherburne@jhuapl.edu, 240-592-1187) is an USAF veteran who previously served as a developmental engineering officer working in high powered electromagnetics and non-destructive testing of aircraft and now works as a RF engineer at JHU/APL.
Works cited
[1] McCue, Ian, Christopher Peitsch, Tim Montalbano, Andrew Lennon, Joseph Sopcisak, Morgana M. Trexler, and Steven Storck. “Scalable laser powder bed fusion processing of nitinol shape memory alloy.” MRS Communications 9, no. 4 (2019): 1214-1220.
[2] McCue, Ian D., Andrew M. Lennon, Drew P. Seker, Chuck Hebert, James P. Mastandrea, Christopher M. Peitsch, Timothy J. Montalbano et al. “Developing Complex Shape-Morphing Metallic Structures for Space Applications.” Johns Hopkins APL Technical Digest (Applied Physics Laboratory) 35, no. 4 (2021): 404-408.
[3] McCue, Ian D., Gianna M. Valentino, Douglas B. Trigg, Andrew M. Lennon, Chuck E. Hebert, Drew P. Seker, Salahudin M. Nimer, James P. Mastandrea, Morgana M. Trexler, and Steven M. Storck. “Controlled shape-morphing metallic components for deployable structures.” Materials & Design 208 (2021): 109935.
[4] Michael Sherburne, Kyle Sibert, Mary Daffron, Andrew Lennon, Howard Feldmesser, Josh Furer, Katherine Wolff, Kevin Pionke, Paul Biermann, Louis Bettwy, Daniel Eby, Chuck Hebert, Samuel Gonzalez, David Grim, Steven Storck, and Jennifer Hollenbeck ACS Applied Engineering Materials 2025 3 (1), 44-50
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