Characterization of Liquid Metal Ink for Stretchable RF Applications

Advances in flexible hybrid electronics have ushered in a range of new applications from ultra-stretchable circuitry for soft robotics to textile-integrated wearable electronics. The onset of the Internet of Things demands even more from these flex-hybrid electronic materials and devices. Specifically, operation in the gigahertz range for transmission, receiving, and transporting data for high-speed operation and near field communication while still maintaining mechanical compliance will be transformative in many commercial areas such as industrial manufacturing, healthcare, and athletics. In this work, we present a stretchable RF transmission line based on a polymerized liquid metal network (Poly-LMN) patterned onto a stretchable dielectric substrate. The Poly-LMN material has metallic conductivity and notably exhibits a high degree of strain insensitivity that is uniquely well-suited to the requirements of stretchable RF devices. The fabrication and characterization of coplanar waveguide transmission lines are presented. The Poly-LMN material maintains consistent transmission and reflection RF performance whereas other stretchable conductors exhibit increased loss while subjecting devices to strains up to 100%. Additional characterization demonstrates the robustness of the chosen material set when subjected to 1,000 cycles of strain and to extreme strains of 300%. Finally, several applications of the stretchable RF conductor are presented, including highly stretchable and self-healing coaxial cables and a peel-and-stick double stub impedance matching system.