3-D Printed Microfluidic Coils With Liquid Metal for Wireless Motion Sensing

Wearable and compliant metallic coils are gaining importance in applications, such as healthcare and Internet of things, for sensing and wireless power and data transfer. This letter presents a resource-efficient and low-cost additive manufacturing (AM)-based microfluidic coils filled with flexible and stretchable liquid metals. The fabrication process involves two main steps: first, printing of the microfluidic capillaries using a stereolithographic 3-D printer, and second, filling the channels with eutectic Gallium-Indium-Tin. We printed the transmitter and receiver coils (resistances 3-5 ohm) and demonstrated wireless power transfer between them with a resonant LC tank circuit. Furthermore, wireless motion sensing is shown with the movement of receiver coil in both horizontal and vertical directions. For vertical motion detection, the peak of the fast Fourier transform signal varies linearly when the coils are separated with steps of 1 mm giving a sensitivity of 1 dBV/mm. The presented approach could extend to develop flexible and squishy metal coils for applications in various fields, such as wearable and implantable electronics, soft robotics, and medical instruments.