Next generation textile‐based wearable sensing systems will require flexibility and strength to maintain capabilities over a wide range of deformations. However, current material sets used for textile‐based skin contacting electrodes lack these key properties, which hinder applications such as electrophysiological sensing. In this work, a facile spray coating approach to integrate liquid metal nanoparticle systems into textile form factors for conformal, flexible, and robust electrodes is presented. The liquid metal system employs functionalized liquid metal nanoparticles that provide a simple “peel‐off to activate” means of imparting conductivity. The spray coating approach combined with the functionalized liquid metal system enables the creation of long‐term reusable textile‐integrated liquid metal electrodes (TILEs). Although the TILEs are dry electrodes by nature, they show equal skin‐electrode impedances and sensing capabilities with improved wearability compared to commercial wet electrodes. Biocompatibility of TILEs in an in vivo skin environment is demonstrated, while providing improved sensing performance compared to previously reported textile‐based dry electrodes. The “spray on dry—behave like wet” characteristics of TILEs opens opportunities for textile‐based wearable health monitoring, haptics, and augmented/virtual reality applications that require the use of flexible and conformable dry electrodes.
Skin-mounted wearable electronics are attractive for continuous health monitoring and human-machine interfacing. The commonly used pre-gelled rigid and bulky electrodes cause discomfort and are unsuitable for continuous long-term monitoring applications. Here, we design carbon nanotubes (CNTs)-based electrodes that can be fabricated using different textile manufacturing processes. We propose woven and braided electrode design using CNTs wrapped textile yarns which are highly conformable to skin and measure a high-fidelity electrocardiography (ECG) signal. The skin-electrode impedance analysis revealed size-dependent behavior. To demonstrate outstanding wearability, we designed a seamless knit electrode that can be worn as a bracelet. The designed CNT-based dry electrodes demonstrated record high signal-to-noise ratios and were very stable against motion artifacts. The durability test of the electrodes exhibited robustness to laundering and practicality for reusable and sustainable applications.
A new design for a quasi-endfire spoof surface plasmon polariton (SSPP) leaky-wave antenna (LWA) is designed for wearable application. The antenna consists of an ultra-thin corrugated metallic structure screen-printed on a flexible textile substrate, which supports extremely confined spoof surface plasmon polaritons. To enable a highly directional leaky mode, two unit-cell designs with different surface impedances are incorporated to realize binary perturbations on the in-plane wavenumber. An auto-adaptive multi-objective optimizer (MOO) is utilized to intelligently design the surface impedance configuration, which achieves significant dimensional reduction compared to the periodically modified SSPP LWAs. A final miniaturized version with 28-unit-cells achieved about 70% size reduction in comparison to the longer design of 75 unit-cells. For proof of concept, the antenna is designed and optimized for operation at 6 GHz. A bandwidth of >200 MHz (5.90 GHz -6.13 GHz) is achieved, centered around 6 GHz, for which the highly directional endfire pattern can be tilted to 22° and 14° for the 28 and 75 unit-call designs, respectively. The measured results agree well with the simulations. Meanwhile, experimental results show that the Specific Absorption Rate (SAR) is lower than 1.6 W/kg standard when the antenna is 2 mm away from the human phantom. This textile-based antenna realized with advanced screen-printing technology is extremely suitable for garment integration due to its high flexibility, low-profile, good fabrication accuracy, and robustness in its performance.INDEX TERMS Leaky-wave antenna, spoof surface plasmon, surface wave, wearable antennas.
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