Physically Reconfigurable RF Liquid Electronics via Laplace Barriers

Liquid metals such as gallium alloys have a unique potential to enable fully reconfigurable RF electronics. One of the major drawbacks for liquid-metal electronics is their interaction with solid-metal contacts, which results in unwanted changes to the electrical performance and delamination of solid-metal contacts due to atomic diffusion of gallium at the liquid-solid interface. In this article, we present a solution to this problem, namely, Laplace barriers, which demonstrate reversible liquid-metal-to-liquid-metal RF connections that provide pressure-directed control of the fluids. While the effect of these channel designs provide superior control over the fluid's position, their effect on RF transmission has not been explored, and the inherent trade space between the microfluidic design and RF performance has never been detailed. RF tunability is demonstrated by fabricating, testing, and modeling a reconfigurable RF microstrip transmission line with integrated the Laplace barriers which operates between 0.5 and 5 GHz. The effect of the Laplace barrier length on both fluidic control and RF performance is reported and compared with the extreme example of a tapered line, which is analogous to a single elongated gap between two Laplace barriers. This approach opens the potential for future all-liquid reconfigurable RF electronic circuits where physical connections between solid and liquid metals are minimized or possibly eliminated.