While 5G is tasked to transform our lives for the better over the next 10 years, next-generation mobile communications, a.k.a. 6G, will undoubtedly demand even higher energy and spectral efficiencies capable of providing myriads of new services and experience to users everywhere they go. Although our technologies do evolve from one generation to the next, the root of the ambition in mobile communications has always been to ensure reliable performance from an uncertain, fluctuating medium. The previous generations have already seen numerous technologies such as advanced coding and signal processing, resource allocation, and most famously, multiple-input multiple-output to redeem some stability from the wireless medium. Inevitably, 6G will be built upon further disruptive technologies that enable another cycle of revolution. In this article, we examine one emerging technology, referred to as fluid antenna system that represents any software-controllable fluidic, conductive, or dielectric structure that can alter its shape and position to reconfigure the gain, radiation pattern, operating frequency, and other characteristics. Fluid antenna takes inspiration from Bruce Lee's Jeet Kune Do to innovate mobile communication systems design. In Bruce Lee's philosophy, one can imitate water to adapt combat style, whereas fluid antenna exploits the dynamic nature of fluids or switchable pixels to achieve ultimate flexibility for diversity and multiplexing benefits that have been unseen before in mobile devices, and the implication can be transformative. This article discusses the potential of fluid antenna systems for 6G, and in particular, we introduce six research topics in fluid antenna systems that if solved successfully could revolutionize mobile communications network design and optimization. This article intends to stimulate discussion that will help shape the development of 6G technologies.

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In this paper, a reconfigurable fluid antenna that utilizes continuous electrowetting (CEW) techniques for achieving agile radiation pattern was presented. The proposed CEW method can electronically shift the position of the liquid metal on the surface-wave antenna. The travelling speed of the liquid metal when immersed in sodium hydroxide electrolyte of different concentrations, and biased under different control signal voltages and waveforms have been experimentally evaluated, the results show that the maximum travelling speed of the liquid metal is about 10 mm.s -1 . The antenna operates in a wide frequency range from 23.5 to 38 GHz, which covers the Very High 5G Frequency band in the different countries. The simulation results show that the addition of CEW geometry will not significantly affect the overall performance of the antenna.

Liquid-based antennas promise to overcome crucial limitations of traditional solid-based ones. Here, we describe different liquid antenna technologies that can be used to build arrays with the unprecedented flexibility and adaptivity needed to enable an evolution in wireless communications. We focus on two approaches which use either metallic or non-metallic liquids as radiating elements. In both cases, the resulting devices can be reconfigured dynamically, thus, modifying the radiation parameters of an antenna in real time in an inexpensive way. To that end, we describe some of the challenges that arise when integrating such antennas as part of a whole communication system. We discuss the solutions adopted in some initial prototypes and summarize some of the problems that need to be solved to pave the way for integrating fully reconfigurable liquid antenna arrays in wireless communication systems.

This paper proposed to use surface wave fluid antennas to realize beam-steering functionality and spatial diversity. By utilizing the advantage of the non-radiating feature of surface wave propagation, in contrast to the conventional multiple RF input ports approach reported, the proposed design only required one RF input to achieve the spatial diversity. The proposed surface wave fluid antenna is designed to work in the millimeter-wave frequency band from 20 to 26.5 GHz. The preliminary results show that the radiation direction of the antenna can be controlled by changing the position of the fluid metal radiator.