3D Printed Liquid Metal Litz Wire for Efficient Wireless Power Transmission

Liquid metals such as eutectic indium gallium (EGaIn) are ideal materials for making low-resistance transmission lines for stretchable and flexible electronics. EGaIn-based passive components like inductors are intriguing due to their conformability, but their lower conductivity limits their RF performance versus Cu. Here, we explore through Finite Element Analysis (FEA) simulations and experiments how multistrand 3D-printed transmission lines can enhance the resonant performance of liquid metal inductors at MHz frequencies. We report multistrand litz-wire, standard litz, and hollow litz geometries for liquid metal coils to boost the Quality Factor (Q) at 1–100 MHz. The smaller litz strands' higher surface area reduces AC resistance and results in a more uniform current density distribution. Our skin-effect optimized design of a litz coil exhibits an inductance of 172 nH at 13.56 MHz and a peak Q that is 50% greater than the Q of standard liquid metal wire, 2X beyond any reported stretchable coils. We also show that enhancement to the coil resonance increases wireless power transmission efficiency by 25% in the MHz-range for applications demanding stretchability.