In the past 10-15 years, non-toxic gallium based liquid metals such as Galinstan and EGaIn have driven a resurgence of studies for new applications in liquid-metal electronics. These applications include inductors, reconfigurable antennas and a liquid metal phase shifter envisioned in 2013. This phase shifter consisted of a liquid metal center conductor encased in an elastic polymer and surrounded by a shield consisting of five hand-woven liquid metal strands also encased in the elastic polymer. While the design was a good proof of concept, it suffered from transverse electromagnetic (TEM) breakdown at high frequencies, as admitted by the authors. This caused increased transmission loss above 2 GHz. What is needed to overcome these pitfalls, making the liquid metal phase shifter a practical device, is a design that reduces these high frequency transmission losses.
Researchers at the University of New Mexico have developed a stretchable liquid metal coaxial phase shifter constructed of a liquid metal center conductor, a liquid metal shield in the shape of a hollow cylinder, and a stretchable rubber- based polymer (EcoflexTM 00-30) which encases and insulates the liquid metal. The ability to apply a stretchable polymer opens new potential applications. By injecting the liquid metal in an elastic polymer container, various different shapes can be made and due to the stretchability, the electrical characteristics can be modified. The design builds on and enhances previous research consisting of the same liquid metal phase shifter but with the shield consisting of five hand-woven liquid metal strands. By modifying the design of the shield to consist of a hollow cylinder rather than woven strands, TEM breakdown at high frequencies is decreased, and the phase shifter improves its transmission and reflection coefficients at higher frequencies.