Broadband Low-Loss On-Body UHF to Millimeter-Wave Surface Wave Links Using Flexible Textile Single Wire Transmission Lines

Abstract

On-body transmission represents a challenge due to human body shadowing. This paper proposes a Sommerfeld-Goubau single-wire transmission line (SWTL) implemented using electronic textiles for low-loss on-body links up to millimeterwave frequencies, overcoming the spherical spreading loss and on-body absorption. The SWTL is fabricated using a conductive thread suitable for embroidery on textiles. A compact tapered launcher is implemented on a flexible polyimide substrate to excite the surface mode along the SWTL. In space, a 3 m-long line maintains a forward transmission over −10 dB between 1 and 3 GHz. The SWTL link is characterized for different body parts showing under 20 dB insertion loss with a 1 cm air gap. Across the torso, a forward transmission over −20 dB is maintained from 0.5 to 2.5 GHz, which represents at least 20 dB improvement over two antennas, of larger dimensions, over-the-air. Directly on-skin, the SWTL can be used around 1 GHz with an S21 over −25 dB, over 50 dB improvement over two on-skin antennas. At 50 GHz, the shielded SWTL exhibits an ultra-low on-body attenuation around 0.11 dB/mm, a four-fold improvement over a microstrip line on the same substrate. It is concluded that SWTLs can enable ultra high-speed future body area networks.

Towards Multi-Mode Millimeter Wave Body Area Networks for Information and Power Transmission: A Co-Existence Study

“…2(c), the SWTL maintains a stable and uniform phase response, i.e. group delay, making it suitable for wide-band communication [13]. However, while a relatively low cross-talk between colocated SWTLs was previously observed [13], the interaction between the SWTL and other antennas remains unknown.…”

“…group delay, making it suitable for wide-band communication [13]. However, while a relatively low cross-talk between colocated SWTLs was previously observed [13], the interaction between the SWTL and other antennas remains unknown. The coupling between the on-body SWTL-supported on-body link and co-located off-body/body-to-body antennas is reported in the next section.…”

“…For high-speed mmWave communication to take place between on-body devices, a low-loss on-body mmWave signalling mechanism is required. A state-of-the-art textile-based SWTL, of approximately 45 cm (inclusive of the coplanar waveguide feed and tapered launchers) is used in this work to realize the on-body mmWave link [13]. While the SWTL is not a wireless transmission mechanism, high-frequency wave-guiding mechanisms using slow-wave lines have been reported for a variety of on-body sensing applications without affecting the user's experience [11].…”

“…While the SWTL offers significantly improved confinement over radiative propagation, it still suffers from higher spurious radiation than a conventional microstrip or coplanar waveguide [13], [19]. To understand the impact of closely-spaced antennas and transmission lines in a multi-mode BAN, the mutual coupling between the SWTL and the microstrip antenna has been experimentally measured in the configuration shown in Fig.…”

“…On the other hand, nonradiative means have been proposed for wearable applications based on surface wave propagation [11], [12], but the reported approaches were narrow-band and limited to sub-6 GHz applications. Recently, a shielded broadband Single Wire Transmission Line (SWTL) has been realized with low loss compared to microstrip lines and wireless up to 50 GHz [13], presenting nearly 4× lower attenuation than a microstrip line on the same substrate.…”