A skin-attachable, stretchable integrated system based on liquid GaInSn for wireless human motion monitoring with multi-site sensing capabilities

This paper introduces a liquid-metal integrated system that combines soft electronics materials and engineering designs with advanced near-field-communication (NFC) functionality for human motion sensing. All of the active components, that is, strain sensor, antenna and interconnections, in this device are made of liquid metal, and the device has unique gel-like characteristics and stretchability. Patterning procedures based on selective wetting properties of the reduced GaInSn enable a skin-attachable, miniaturized layout, in which the diameter of the device is less than 2 cm. Electromechanical characterization of the strain sensor and antenna reveals their behaviors under large uniaxial tensile and compressive strains, as well as more complex modes of deformation. Demonstrations of these devices involve their use in monitoring various human motions in a purely wireless fashion; examples include wrist flexion, movements of the vocal cord and finger motion. This simple platform has potential for use in human–machine interfaces for prosthetic control and other applications. Stretchable electronics: Liquid metals have reach-out-and-touch appeal A battery-free sensor that wirelessly transmits data while attached to skin relies on unique liquid-gallium materials for its success. Unlike liquid mercury, gallium is safe to handle in ambient conditions and hence is suitable for use in devices that seek to conform to the soft contours of the human body while remaining conductive. Jeong Sook Ha from Korea University and colleagues designed special patterns in polydimethylsiloxane films to create a liquid-metal strain sensor with a built-in antenna. By removing an outer oxide crust that adheres to nearly any surface, the team solved problems associated with patterning difficult-to-treat bare liquid metals. They demonstrated that changes in resistance from the gel-like sensor could accurately measure wrist motion, vocal cord movement associated with speech and the condition of finger joints. A gallium-based liquid metal integrated system that combines soft electronics materials and engineering designs with advanced near-field-communication (NFC) functionality is reported. Electro-mechanical characterization of the device reveals their behaviors under large uniaxial tensile and compressive strains, as well as more complex modes of deformation. Demonstrations of these devices involve their use in monitoring of various human motions in a purely wireless fashion.