Wireless charging and readout via textile coil for continuous full-body wearable computing

TL;DR

The paper addresses the battery burden in wearable computing by proposing a body-scale meander textile coil that confines inductive fields to near the body to enable safe, efficient wireless charging (W-class) and battery-free, low-power readout (uW-class) across the body. It presents two implementations—the liquid-metal-based meander coil++ and the automated machine-knitted twin meander coil—demonstrating high-efficiency charging and passive readout with PIT, supported by NFC-compatible tuning and safety considerations. The coils provide broad body coverage (around 70%) and manufacturability on knitting machines, enabling battery-free, continuous full-body wearable computing in everyday clothing. This work advances practical, scalable textile-based wireless power/data networks for pervasive wearable devices.

Abstract

The growing use of wearable devices for activity tracking, healthcare, and haptics faces challenges due to the bulkiness and short lifespan of batteries. Integration of a textile-based wireless charging and readout system into everyday clothing can enable seamless power supply and data collection around the body. However, expanding such system to cover the entire body is challenging, as it increases electromagnetic interference with the body, degrading the performance of wireless system. This article introduces a meandered textile coil designed for body-scale, efficient wireless charging and readout. The meander coil can confine a strong inductive field near the body surface, ensuring W-class safe charging and sensitive readout with uW-class low power. Moreover, its zigzag design is simple enough for mass production on industrial knitting machines. Therefore, the body-scale meander coil can continuously operate battery-free wearable devices across the body, leading to ubiquitous deployment of continuous full-body wearable computing into everyday clothing.

Figures (3)

• Figure 1: Illustration of textile-based wireless charging and readout. A gray-colored electric textile connected to a mobile battery can construct wireless power transfer and data collection scheme for on-body wearable devices throughout the textile. Such clothes has the potential to allow a battery-free, lightweight design of wearable device operating onto the body for days and weeks.
• Figure 2: Overview of wireless charging and readout using a body-scale meandered textile coil. (a) Illustration of meandered textile coil. (a) Illustration of wiring structure of helical or meander coil and (b) their simulated inductive field pattern near the simplified circular body model. (c) Technical comparison of the meandered textile coil with prior approaches in terms of DC-to-DC power transfer efficiency and coverage area of the body.
• Figure 3: Examples of meandered textile coil. (a) Liquid-metal-based meander coil named meander coil++ can safely and efficiently send -class power to the wearable devices. The output power indicates the transferred power from the meander coil++. (b) Machine-knitted meander coil named twin meander coil can provide a fast and automatic fabrication of the meandered textile coil with a minimal post processing, in addition to supporting -class wireless readout of battery-free wearable sensors. The wearable sensors include four sensor coils, each of which can superimpose ID, touch, discrete rotation, or pressure value into a unique passive response, have different resonant frequencies for the twin meander coil to recognize the sensor's type.