Stretchable Microwave Transmission Lines Using Liquid‐Metal Embedded Elastomers

Abstract

The characterization of an RF transmitter composed of insulating and conducting regions of liquid‐metal embedded elastomer (LMEE) is presented along with in situ measurements of LMEE microstrip lines as they are subjected to local material strains up to 40%. The LMEE is comprised of microscale droplets of a gallium–indium alloy that is liquid at room temperature and suspended within a cured elastomer matrix of polydimethylsiloxane (PDMS). The liquid metal microparticles were initially electrically isolated, but applying mechanical loading caused the permanent formation of highly localized conductive traces. Bonding films of LMEE onto a PDMS dielectric layer resulted in a stretchable microstrip structure that is capable of radio frequency (RF) transmission. Scattering parameter (S‐parameter) measurements for reflection and transmission are presented for these microstrip lines as the electrical length increased up to 19%. A customized clamp was utilized to isolate the mechanical strain on the material from the electrical connectors and allow for transmission line characterization under applied strain and dielectric characterization of the LMEE material was performed. The stretchable microstrip lines show remarkable consistency in transmission response at 0.5–5 GHz when mechanically loaded to 40% strain for 1000 loading cycles.