As a midwestern woman who is perpetually cold, even in the summer, there are few things I love more than a cozy sweater. A well-knit sweater is like a warm hug from a fashionable friend. Despite my love for this ubiquitous garment, it had never occurred to me that a humble sweater could be upgraded and optimized with the latest technology. In the not-too-distant future, my favorite Fair Isle sweater could double as a communication device.

A team of researchers at Columbia Engineering have created lightweight, flexible radio-frequency (RF) communications antennas that can disseminate information over long distances. To achieve this outcome, the team combined metasurfaces, which are ultra-thin optical components that can control the propagation of light, with a flat-knitting platform. This allows the team to marry the RF properties of traditional rooftop dish antennas with wearable, knitted objects like sweaters and blankets.

Before work began on the project, the research team studied various knitting and weaving techniques, two common approaches for creating patterned textiles. Ultimately, the researchers decided to use the float-jacquard knitting technique, which utilizes two or more types of yarn to create the pattern. What makes this approach unique is that a yarn is floated loose beneath the fabric when not used and transferred back to the frontside as needed to create the desired pattern. The team then incorporated metallic and dielectric yarns to produce two prototype reflectarray devices, a metasurface lens (metalens) and a vortex-beam generating device.

The team recently published their findings in Advanced Materials. The paper, titled “Flat-Knit, Flexible, Textile Metasurfaces,” was authored by researchers Michael J. Carter, Leah Resneck, Younes Ra'di, and Nanfang Yu. In an excerpt from the abstract, the team writes: “Operating as a receiving antenna, the metalens focuses a collimated normal-incidence beam to a diffraction-limited, off-broadside focal spot. Operating as a transmitting antenna, the metalens converts the divergent emission from a horn antenna into a collimated beam with peak measured directivity, gain, and efficiency of 21.30, 15.30, and −6.00 dB (25.12%), respectively. The vortex-beam generating metasurface produces a focused vortex beam with a topological charge of m = 1 over a wide frequency range of 4.1–5.8 GHz. Strong specular reflection is observed for the textile reflectarrays, caused by wavy yarn floats on the backside of the float-jacquard textiles.”

In a recent quote, Nanfang Yu, associate professor of applied physics and applied mathematics, said, “It’s important to stress that these devices were fabricated using commercially available off-the-shelf yarns and leveraging established fabrication techniques. I am almost certain that communities of knitters can come up with ingenious ways to integrate aesthetics and functionality into a sweater – a sweater that can double as a WiFi signal booster.”