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.

Design and Fabrication of Stretchable Microwave Transmission Lines Based on a Quasi-Microstrip Structure

“…Figure b shows that the insertion loss increased for longer transmission lines; however, the longest line (8 turns) exhibited an insertion loss of only −3.46 dB at 40 GHz, which was the lowest compared with those of other demonstrated stretchable RF transmission lines. A comparison between this work and other previously reported stretchable transmission lines is shown in Table S1. − As shown in Figure c, the return loss characteristics followed a similar trend up to 10 GHz; however, beyond that range, the loss characteristics resonated without a trend, owing to the impedance mismatch. Figure d shows the electrical resistances of the two conductor layers (signal and ground) for different numbers of serpentine turns.…”