3D Woven Liquid Metals for High-Frequency Stretchable Circuits

Abstract

Mechanically flexible and stretchable inductive coils are a critical component for enabling communication, sensing, and wireless power transfer capabilities in future wearable electronic devices that conform to the body for healthcare and the Internet of Things (IoT) applications. However, the mechanical conformability of leading stretchable materials such as liquid metals (LMs) sacrifices electromagnetic performance since conductivity lags behind conventional rigid Cu wires, leading to lossy radio-frequency (RF) characteristics. Here, we present a strategy leveraging multistranded three-dimensional (3D) woven 'litz' transmission lines to amplify the resonant RF performance of LM inductors. Through comprehensive simulations and experiments, we discovered that interwoven LM litz wires boost the Quality Factor (Q) by 80 % compared to standard liquid metal wires. We also demonstrate a fabrication methodology for stretchable coils that retain high Q (>30), outperforming the previously reported LM coils and maintaining 98 % of their wireless transmission efficiency under up to 30 % biaxial strain. Moreover, we showcase the versatility of this approach by 3D printing four-terminal 'choke' inductors optimized for RF filtering and inductance tunability, overcoming the fabrication limitations of traditional planar printed electronics. These results offer valuable insights into the design and implementation of 3D-printed magnetics for a diverse suite of electromagnetic device applications.