2023 Theses Doctoral

Lightweight and Flexible Textile Metasurfaces and Array Antennas via Flat-Knitting

Carter, Michael Joseph

Metasurfaces are a class of electromagnetic devices that shape an outgoing wavefront to realize desired device functionalities. The predominant majority of current generation metasurfaces are compact, planar rigid devices that aim to replace traditional bulk optical components and radio-frequency antennae. The development of lightweight and flexible metasurfaces could enable new classes of conformal metasurfaces that can be used to cover non-planar surfaces in applications such as wearable antennas or carpet cloaks and also help further reduce the weight of existing planar rigid devices and enable easy stowage of very large aperture devices, possibly leading to a new class of lightweight, easily stowable and deployable devices, useful in both terrestrial and space-based communications and sensing applications.

Textiles represent an interesting platform for lightweight and flexible metasurfaces. Leveraging highly-established fabric production techniques such as knitting, weaving, and embroidery could enable the production of relatively cheap, flexible devices on an industrial scale. Knitting, in particular, represents a highly-established and highly-flexible fabric production technique capable of engineering the shape and mechanical properties of the fabric alongside the fabric's electromagnetic response via patterning the fabric with metallic antenna archetypes.

The works presented in this thesis aim to demonstrate novel designs and means to fabricate flexible, lightweight metasurfaces and array antennas that rely on scalable, established production techniques and commercially available materials. Further aims of this thesis are to provide a detailed account of the fabrication, design, and performance of textile metasurfaces and array antennas and provide limited commentary on the commercial prospects, limitations, and fabrication demands of the works presented herein.

The first works detailed in this thesis concern a novel type of lightweight and flexible metasurface produced via flat-knitting using float-jacquard colorwork knitting to pattern the fabric with an array of antenna archetypes. This includes novel demonstrations of a textile metalens and textile metasurface vortex beam generator capable of producing, respectively, focused or collimated Gaussian and vortex beams, albeit with low efficiency. Detailed modeling and analysis of the structure of the float-jacquard knit flexible metasurfaces identify a key cause of the degraded performance of these devices, the irregular float geometry, in particular contact between metallic floats that give rise to a strong specular reflection, offering insight into future avenues for further optimization.

The second work detailed in this thesis concerns a flat-knit flexible array antenna consisting of four Yagi-Uda antennas. A different colorwork knitting approach, intarsia knitting, is used to pattern the antenna elements into the fabric. The intarsia knit flexible array antenna performs comparably to other flexible end-fire antennas with a gain of 6.94 dB and forward-to-backward power ratio of 9.25 dB, offering a compelling platform for small arrays of flexible antennas, which can be integrated into wearable garments and textiles.

The final work detailed in this thesis concerns another flat-knit flexible metasurface, a metalens, knit using intarsia colorwork. The intarsia knit metasurface has a peak focusing efficiency of 47.46%, and, when oriented as reflectarray, a peak gain of 24.71 dB. The large aperture intarsia knit flexible metasurfaces demonstrate comparable performance to existing flexible metasurfaces, making them far more suitable for commercial applications, albeit with higher fabrication demands than float-jacquard knit devices.