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Researchers have designed and demonstrated stretchable waveguides that maintain efficient, stable signal transmission of surface plasmon polaritons even when bent, twisted or stretched. These plasmonic waveguides could make it possible to seamlessly embed advanced sensing, communication and health monitoring functions into everyday wearable materials.

Plasmonic waveguides are tiny structures that guide light by coupling it with electrons on a metal surface. The new flexible waveguides transmit what are known as spoof surface plasmon polaritons, which are formed with longer wavelengths—radio frequencies in this case—rather than the conventional infrared or visible light.

"Although our work is still at the research stage, it highlights the exciting possibility of merging advanced electromagnetic technologies with soft, stretchable materials," said research team leader Zuojia Wang from Zhejiang University. "This brings us closer to a future where advanced health care and connectivity are integrated into what we wear."

In the journal Optical Materials Express, the researchers their elastic spoof surface plasmonic waveguides, which fully recover their original size and shape after being stretched. They experimentally show that the waveguides achieve stable signal transmission with high efficiency and strong electromagnetic energy confinement even when stretched or bent.

"Stretchable plasmonic waveguides could one day be integrated into wearable and textile-based devices that monitor vital signs, support wireless communication or enable unobtrusive health tracking," said Wang. "This technology might also eventually contribute to more comfortable, reliable and body-compatible electronics—such as smart clothing for continuous medical monitoring, soft communication devices for emergencies or flexible interfaces that connect humans with machines and robots."

Bendable waveguides

Compared to their infrared and visible counterparts, spoof surface plasmons are easier to integrate with electronics, can enable smaller devices, and can better penetrate materials like plastics and clothing. Although this has made them attractive for textile-based sensing, it has been difficult to create stretchable conductive materials capable of generating and controlling these plasmons.

To overcome this limitation, the researchers developed a new design that helically winds deformable metallic wires onto thermoplastic polyurethane to create flexible waveguides. This approach provides both elastic recovery and excellent compatibility with fabric and skin. The design also improves mechanical stability compared to other stretchable substrates by reducing lateral strain during longitudinal stretching.

"Our work demonstrates that plasmonic waveguides can be designed with inherent stretchability while still maintaining robust electromagnetic performance," said Wang. "Beyond fundamental plasmonics, this approach could enable adaptive wireless communication, body-compatible sensors and conformal devices that seamlessly interface with biological tissues or dynamic surfaces."

Signals that stretch

To experimentally validate the plasmonic waveguides, the researchers fabricated prototypes and measured their electric field distributions while connected to specialized test equipment.

The experiments showed that the waveguides could stretch up to 50% without changing width (zero Poisson's ratio) and that signal transmission varied by no more than 10% when stretched. The waveguides also continued to transmit efficiently even when bent or twisted.

The researchers are now integrating these waveguides into a chest strap prototype that uses electromagnetic metafabric to detect human heartbeats. They also plan to explore advanced textile techniques, incorporating finer microstructures—such as microknots and helical microwires—to enhance the mechanical performance of smart textile systems.