Ancient 3D paper art used to make microwave antennas

Researchers at Drexel University and The University of British Columbia (UBC) believe kirigami, the ancient Japanese art of cutting and folding paper to create intricate three-dimensional designs, could provide a model for manufacturing the next generation of antennas.

The team has already demonstrated how kirigami, which is a variation of origami, can transform a single sheet of acetate coated with conductive MXene ink into a flexible 3D microwave antenna whose transmission frequency can be adjusted simply by pulling or squeezing to slightly shift its shape. Their proof of concept, showcased in the journal Nature Communications, represents a new way to quickly and cost-effectively manufacture an antenna by simply coating aqueous MXene ink onto a clear elastic polymer substrate material.

The future of wireless technology — from charging devices to boosting communication signals — relies on the antennas that transmit electromagnetic waves becoming increasingly versatile, durable and easy to manufacture. As noted by study co-author Professor Yury Gogotsi, from Drexel’s College of Engineering, “For wireless technology to support advancements in fields like soft robotics and aerospace, antennas need to be designed for tuneable performance and with ease of fabrication. Kirigami is a natural model for a manufacturing process, due to the simplicity with which complex 3D forms can be created from a single 2D piece of material.”

Standard microwave antennas can be reconfigured either electronically or by altering their physical shape. However, adding the necessary circuitry to control an antenna electronically can increase its complexity, making the antenna bulkier, more vulnerable to malfunction and more expensive to manufacture. By contrast, the process demonstrated in this joint work leverages physical shape change and can create antennas in a variety of intricate shapes and forms. These antennas are flexible, lightweight and durable, which are crucial factors for their survivability on movable robotics and aerospace components.

To create the test antennas, the researchers first coated a sheet of acetate with a special conductive ink, composed of a titanium carbide MXene, to create frequency-selective patterns. MXenes are a family of two-dimensional nanomaterials whose physical and electrochemical properties can be adjusted by slightly altering their chemical composition; MXene ink is particularly useful in this application because its chemical composition allows it to adhere strongly to the substrate for a durable antenna and can be adjusted to reconfigure the transmission specifications of the antenna.

Using kirigami techniques, originally developed in Japan in the fourth and fifth centuries, the researchers made a series of parallel cuts in the MXene-coated surface. Pulling at the edges of the sheet triggered an array of square-shaped resonator antennas to spring from its two-dimensional surface. Varying the tension caused the angle of the array to shift — a capability that could be deployed to quickly adjust the communications configuration of the antennas.

The researchers assembled two kirigami antenna arrays for testing. They also created a prototype of a co-planar resonator — a component used in sensors that naturally produces waves of a certain frequency — to showcase the versatility of the approach. In addition to communication applications, resonators and reconfigurable antennas could also be used for strain-sensing, according to the team.

“Frequency selective surfaces, like these antennas, are periodic structures that selectively transmit, reflect or absorb electromagnetic waves at specific frequencies,” said Mohammad Zarifi, principal research chair and associate professor at UBC, who helped lead the research. “They have active and/or passive structures and are commonly used in applications such as antennas, radomes and reflectors to control wave propagation direction in wireless communication at 5G and beyond platforms.”

The kirigami antennas proved effective at transmitting signals in three commonly used microwave frequency bands: 2–4 GHz, 4–8 GHz and 8–12 GHz. Additionally, the team found that shifting the geometry and direction of the substrate could redirect the waves from each resonator. The frequency produced by the resonator shifted by 400 MHz as its shape was deformed under strain conditions — demonstrating that it could perform effectively as a strain sensor for monitoring the condition of infrastructure and buildings.

According to the team, these findings are the first step towards integrating the components on relevant structures and wireless devices. With kirigami’s myriad forms as their inspiration, the team will now seek to optimise the performance of the antennas by exploring new shapes, substrates and movements.

“Our goal here was to simultaneously improve the adjustability of antenna performance as well as create a simple manufacturing process for new microwave components by incorporating a versatile MXene nanomaterial with kirigami-inspired designs,” said UBC’s Dr Omid Niksan, an author on the paper. “The next phase of this research will explore new materials and geometries for the antennas.”

Image courtesy Drexel University